Minor fix to python table caching API.
Minor fix to python table caching API.

Author: Michael Armbrust <michael@databricks.com>

Closes #585 from marmbrus/pythonCacheTable and squashes the following commits:

7ec1f91 [Michael Armbrust] Minor fix to python table caching API.

tejasapatil/spark,shubhamchopra/spark,jiangxb1987/spark,debugger87/spark,highfei2011/spark,hvanhovell/spark,skonto/spark,ioana-delaney/spark,akopich/spark,kiszk/spark,nchammas/spark,liutang123/spark,dhruve/spark,rednaxelafx/apache-spark,kimoonkim/spark,someorz/spark,SnappyDataInc/spark,sahilTakiar/spark,rekhajoshm/spark,skonto/spark,goldmedal/spark,WeichenXu123/spark,zuotingbing/spark,sureshthalamati/spark,hhbyyh/spark,wangyum/spark,ddna1021/spark,someorz/spark,caneGuy/spark,mdespriee/spark,lxsmnv/spark,aokolnychyi/spark,goldmedal/spark,srowen/spark,minixalpha/spark,zhouyejoe/spark,michalsenkyr/spark,milliman/spark,ueshin/apache-spark,saltstar/spark,eyalfa/spark,saturday-shi/spark,darionyaphet/spark,haowu80s/spark,janewangfb/spark,gioenn/xSpark,kimoonkim/spark,wangmiao1981/spark,ptkool/spark,zzcclp/spark,joseph-torres/spark,mike0sv/spark,jiangxb1987/spark,vinodkc/spark,loneknightpy/spark,WindCanDie/spark,rikima/spark,gioenn/xSpark,liutang123/spark,hhbyyh/spark,BryanCutler/spark,michalsenkyr/spark,pgandhi999/spark,jianran/spark,akopich/spark,rezasafi/spark,guoxiaolongzte/spark,mzl9039/spark,chuckchen/spark,taroplus/spark,poffuomo/spark,dongjoon-hyun/spark,dongjoon-hyun/spark,kiszk/spark,akopich/spark,stanzhai/spark,techaddict/spark,zhouyejoe/spark,patrick-nicholson/spark,wangyum/spark,big-pegasus/spark,tejasapatil/spark,icexelloss/spark,bOOm-X/spark,ericvandenbergfb/spark,goldmedal/spark,tejasapatil/spark,mahak/spark,ptkool/spark,apache-spark-on-k8s/spark,JerryLead/spark,esi-mineset/spark,xuanyuanking/spark,big-pegasus/spark,aokolnychyi/spark,WindCanDie/spark,jkbradley/spark,techaddict/spark,cloud-fan/spark,alunarbeach/spark,skonto/spark,akopich/spark,hvanhovell/spark,darionyaphet/spark,markhamstra/spark,andrewor14/spark,nchammas/spark,ConeyLiu/spark,narahari92/spark,Panos-Bletsos/spark-cost-model-optimizer,gioenn/xSpark,caneGuy/spark,ahnqirage/spark,shaneknapp/spark,aosagie/spark,adrian-ionescu/apache-spark,big-pegasus/spark,nchammas/spark,tejasapatil/spark,jrshust/spark,apache-spark-on-k8s/spark,big-pegasus/spark,metamx/spark,nlalevee/spark,MLnick/spark,JerryLead/spark,dhruve/spark,big-pegasus/spark,panfengfeng/spark,liutang123/spark,map222/spark,chuckchen/spark,zuotingbing/spark,big-pegasus/spark,bOOm-X/spark,HyukjinKwon/spark,metamx/spark,maropu/spark,nilsgrabbert/spark,shubhamchopra/spark,milliman/spark,metamx/spark,shubhamchopra/spark,aosagie/spark,1haodian/spark,publicRoman/spark,ioana-delaney/spark,JoshRosen/spark,gioenn/xSpark,zzcclp/spark,ajaysaini725/spark,publicRoman/spark,metamx/spark,rekhajoshm/spark,darionyaphet/spark,jiangxb1987/spark,Aegeaner/spark,xuanyuanking/spark,facaiy/spark,saturday-shi/spark,LantaoJin/spark,pgandhi999/spark,actuaryzhang/spark,nchammas/spark,rikima/spark,ptkool/spark,actuaryzhang/spark,sachintyagi22/spark,witgo/spark,dhruve/spark,MLnick/spark,shuangshuangwang/spark,ron8hu/spark,tejasapatil/spark,jrshust/spark,publicRoman/spark,zhouyejoe/spark,apache-spark-on-k8s/spark,nilsgrabbert/spark,chuckchen/spark,aray/spark,MLnick/spark,andrewor14/spark,setjet/spark,hvanhovell/spark,andrewor14/iolap,BryanCutler/spark,Panos-Bletsos/spark-cost-model-optimizer,saltstar/spark,lvdongr/spark,witgo/spark,zero323/spark,mike0sv/spark,HyukjinKwon/spark,saturday-shi/spark,michalsenkyr/spark,bravo-zhang/spark,cin/spark,icexelloss/spark,tengpeng/spark,UndeadBaneGitHub/spark,kiszk/spark,nilsgrabbert/spark,milliman/spark,ericvandenbergfb/spark,gengliangwang/spark,mdespriee/spark,jkbradley/spark,andrewor14/iolap,facaiy/spark,spark-test/spark,szhem/spark,shaneknapp/spark,guoxiaolongzte/spark,goldmedal/spark,cloud-fan/spark,markhamstra/spark,setjet/spark,wzhfy/spark,mzl9039/spark,liutang123/spark,aray/spark,szhem/spark,aray/spark,zero323/spark,saturday-shi/spark,lxsmnv/spark,aokolnychyi/spark,facaiy/spark,rikima/spark,SHASHANKB/spark,maropu/spark,JerryLead/spark,jianran/spark,UndeadBaneGitHub/spark,rekhajoshm/spark,xflin/spark,adrian-ionescu/apache-spark,byakuinss/spark,LantaoJin/spark,kissmetrics/spark,facaiy/spark,ajaysaini725/spark,wangyum/spark,hhbyyh/spark,tengpeng/spark,janewangfb/spark,UndeadBaneGitHub/spark,bravo-zhang/spark,apache/spark,yanboliang/spark,debugger87/spark,dbtsai/spark,hhbyyh/spark,aosagie/spark,actuaryzhang/spark,gengliangwang/spark,mike0sv/spark,rednaxelafx/apache-spark,ajaysaini725/spark,cloud-fan/spark,BryanCutler/spark,MLnick/spark,jiangxb1987/spark,wangmiao1981/spark,rekhajoshm/spark,nchammas/spark,lxsmnv/spark,kiszk/spark,debugger87/spark,sachintyagi22/spark,nilsgrabbert/spark,brad-kaiser/spark,shaneknapp/spark,hhbyyh/spark,ibm-research-ireland/sparkoscope,jlopezmalla/spark,szhem/spark,minixalpha/spark,ioana-delaney/spark,pgandhi999/spark,ron8hu/spark,shuangshuangwang/spark,spark-test/spark,hhbyyh/spark,ajaysaini725/spark,brad-kaiser/spark,rikima/spark,SnappyDataInc/spark,eyalfa/spark,Panos-Bletsos/spark-cost-model-optimizer,jkbradley/spark,spark-test/spark,hvanhovell/spark,rednaxelafx/apache-spark,gengliangwang/spark,lxsmnv/spark,ueshin/apache-spark,ConeyLiu/spark,WeichenXu123/spark,xflin/spark,SnappyDataInc/spark,cin/spark,panfengfeng/spark,ptkool/spark,aokolnychyi/spark,shuangshuangwang/spark,actuaryzhang/spark,map222/spark,mdespriee/spark,kimoonkim/spark,rednaxelafx/apache-spark,jkbradley/spark,holdenk/spark,JerryLead/spark,UndeadBaneGitHub/spark,huang1900/spark,byakuinss/spark,mahak/spark,srowen/spark,HyukjinKwon/spark,taroplus/spark,nlalevee/spark,icexelloss/spark,goldmedal/spark,panfengfeng/spark,yanboliang/spark,ibm-research-ireland/sparkoscope,setjet/spark,ueshin/apache-spark,apache/spark,shuangshuangwang/spark,zhouyejoe/spark,loneknightpy/spark,ron8hu/spark,lvdongr/spark,patrick-nicholson/spark,kiszk/spark,loneknightpy/spark,rezasafi/spark,spark-test/spark,minixalpha/spark,michalsenkyr/spark,witgo/spark,xuanyuanking/spark,alunarbeach/spark,haowu80s/spark,xuanyuanking/spark,darionyaphet/spark,mzl9039/spark,andrewor14/spark,brad-kaiser/spark,michalsenkyr/spark,andrewor14/iolap,loneknightpy/spark,patrick-nicholson/spark,liutang123/spark,caneGuy/spark,brad-kaiser/spark,cin/spark,ron8hu/spark,sureshthalamati/spark,pronix/spark,facaiy/spark,witgo/spark,cin/spark,kevinyu98/spark,debugger87/spark,wangmiao1981/spark,jianran/spark,holdenk/spark,apache/spark,poffuomo/spark,Aegeaner/spark,rezasafi/spark,rednaxelafx/apache-spark,ConeyLiu/spark,guoxiaolongzte/spark,ddna1021/spark,panfengfeng/spark,yanboliang/spark,janewangfb/spark,jrshust/spark,patrick-nicholson/spark,guoxiaolongzte/spark,saltstar/spark,map222/spark,bOOm-X/spark,andrewor14/iolap,aosagie/spark,wzhfy/spark,maropu/spark,mike0sv/spark,jianran/spark,shaneknapp/spark,szhem/spark,publicRoman/spark,wzhfy/spark,actuaryzhang/spark,jrshust/spark,zzcclp/spark,zzcclp/spark,LantaoJin/spark,someorz/spark,Aegeaner/spark,vinodkc/spark,rekhajoshm/spark,wzhfy/spark,bdrillard/spark,poffuomo/spark,apache-spark-on-k8s/spark,WeichenXu123/spark,jianran/spark,aray/spark,apache/spark,wangyum/spark,highfei2011/spark,pronix/spark,ddna1021/spark,ddna1021/spark,aosagie/spark,WindCanDie/spark,apache/spark,mzl9039/spark,narahari92/spark,chuckchen/spark,LantaoJin/spark,guoxiaolongzte/spark,adrian-ionescu/apache-spark,sureshthalamati/spark,apache-spark-on-k8s/spark,techaddict/spark,andrewor14/spark,witgo/spark,holdenk/spark,wangmiao1981/spark,SHASHANKB/spark,big-pegasus/spark,sachintyagi22/spark,shubhamchopra/spark,rednaxelafx/apache-spark,loneknightpy/spark,ron8hu/spark,jkbradley/spark,kimoonkim/spark,Panos-Bletsos/spark-cost-model-optimizer,patrick-nicholson/spark,mzl9039/spark,lvdongr/spark,szhem/spark,kevinyu98/spark,SnappyDataInc/spark,jiangxb1987/spark,michalsenkyr/spark,aokolnychyi/spark,Aegeaner/spark,huang1900/spark,witgo/spark,kevinyu98/spark,techaddict/spark,highfei2011/spark,milliman/spark,narahari92/spark,taroplus/spark,ddna1021/spark,mahak/spark,zzcclp/spark,nilsgrabbert/spark,JoshRosen/spark,zuotingbing/spark,SHASHANKB/spark,chuckchen/spark,ibm-research-ireland/sparkoscope,highfei2011/spark,sureshthalamati/spark,vinodkc/spark,actuaryzhang/spark,lvdongr/spark,akopich/spark,rekhajoshm/spark,liyichao/spark,ericvandenbergfb/spark,dbtsai/spark,debugger87/spark,holdenk/spark,rezasafi/spark,taroplus/spark,zzcclp/spark,panfengfeng/spark,gioenn/xSpark,poffuomo/spark,bOOm-X/spark,ahnqirage/spark,jlopezmalla/spark,ericvandenbergfb/spark,mahak/spark,huang1900/spark,vinodkc/spark,dongjoon-hyun/spark,darionyaphet/spark,yanboliang/spark,milliman/spark,patrick-nicholson/spark,joseph-torres/spark,ddna1021/spark,esi-mineset/spark,brad-kaiser/spark,kissmetrics/spark,JoshRosen/spark,darionyaphet/spark,taroplus/spark,spark-test/spark,goldmedal/spark,jlopezmalla/spark,esi-mineset/spark,aray/spark,bravo-zhang/spark,SnappyDataInc/spark,sahilTakiar/spark,alunarbeach/spark,dbtsai/spark,panfengfeng/spark,gengliangwang/spark,rikima/spark,alunarbeach/spark,ConeyLiu/spark,MLnick/spark,caneGuy/spark,byakuinss/spark,huang1900/spark,huang1900/spark,kevinyu98/spark,bOOm-X/spark,sahilTakiar/spark,icexelloss/spark,ptkool/spark,shuangshuangwang/spark,mike0sv/spark,facaiy/spark,lxsmnv/spark,cloud-fan/spark,haowu80s/spark,WeichenXu123/spark,map222/spark,witgo/spark,andrewor14/spark,esi-mineset/spark,caneGuy/spark,SHASHANKB/spark,alunarbeach/spark,BryanCutler/spark,pronix/spark,techaddict/spark,stanzhai/spark,lvdongr/spark,bdrillard/spark,jrshust/spark,zuotingbing/spark,ajaysaini725/spark,guoxiaolongzte/spark,poffuomo/spark,gengliangwang/spark,ioana-delaney/spark,sureshthalamati/spark,markhamstra/spark,shaneknapp/spark,LantaoJin/spark,sureshthalamati/spark,mdespriee/spark,rezasafi/spark,zuotingbing/spark,someorz/spark,jlopezmalla/spark,ibm-research-ireland/sparkoscope,spark-test/spark,icexelloss/spark,joseph-torres/spark,szhem/spark,kevinyu98/spark,caneGuy/spark,setjet/spark,minixalpha/spark,ahnqirage/spark,stanzhai/spark,jianran/spark,MLnick/spark,Aegeaner/spark,kissmetrics/spark,zero323/spark,bdrillard/spark,ioana-delaney/spark,WeichenXu123/spark,techaddict/spark,ericvandenbergfb/spark,cloud-fan/spark,akopich/spark,zuotingbing/spark,ConeyLiu/spark,guoxiaolongzte/spark,jiangxb1987/spark,nlalevee/spark,HyukjinKwon/spark,adrian-ionescu/apache-spark,shuangshuangwang/spark,yanboliang/spark,ueshin/apache-spark,someorz/spark,gioenn/xSpark,map222/spark,dbtsai/spark,sachintyagi22/spark,ConeyLiu/spark,joseph-torres/spark,holdenk/spark,eyalfa/spark,pgandhi999/spark,rezasafi/spark,kevinyu98/spark,liyichao/spark,publicRoman/spark,zhouyejoe/spark,xflin/spark,UndeadBaneGitHub/spark,SnappyDataInc/spark,nlalevee/spark,holdenk/spark,andrewor14/iolap,janewangfb/spark,byakuinss/spark,rikima/spark,dhruve/spark,tengpeng/spark,aokolnychyi/spark,markhamstra/spark,xflin/spark,Aegeaner/spark,markhamstra/spark,UndeadBaneGitHub/spark,liyichao/spark,kimoonkim/spark,dhruve/spark,ibm-research-ireland/sparkoscope,minixalpha/spark,bdrillard/spark,szhem/spark,wangmiao1981/spark,aokolnychyi/spark,bdrillard/spark,liyichao/spark,BryanCutler/spark,hvanhovell/spark,pgandhi999/spark,tejasapatil/spark,chuckchen/spark,mdespriee/spark,narahari92/spark,kissmetrics/spark,andrewor14/iolap,BryanCutler/spark,highfei2011/spark,taroplus/spark,michalsenkyr/spark,kissmetrics/spark,maropu/spark,maropu/spark,bdrillard/spark,zzcclp/spark,zero323/spark,zhouyejoe/spark,alunarbeach/spark,ericvandenbergfb/spark,sahilTakiar/spark,srowen/spark,JoshRosen/spark,dongjoon-hyun/spark,narahari92/spark,wzhfy/spark,wzhfy/spark,aosagie/spark,poffuomo/spark,ajaysaini725/spark,SHASHANKB/spark,wzhfy/spark,apache-spark-on-k8s/spark,JoshRosen/spark,techaddict/spark,JoshRosen/spark,haowu80s/spark,jlopezmalla/spark,setjet/spark,WindCanDie/spark,highfei2011/spark,andrewor14/spark,wangmiao1981/spark,janewangfb/spark,HyukjinKwon/spark,WeichenXu123/spark,1haodian/spark,lvdongr/spark,tejasapatil/spark,liyichao/spark,JoshRosen/spark,ueshin/apache-spark,joseph-torres/spark,saltstar/spark,janewangfb/spark,dbtsai/spark,holdenk/spark,xuanyuanking/spark,someorz/spark,liyichao/spark,sahilTakiar/spark,goldmedal/spark,darionyaphet/spark,srowen/spark,xuanyuanking/spark,apache/spark,SHASHANKB/spark,pronix/spark,ioana-delaney/spark,haowu80s/spark,vinodkc/spark,dbtsai/spark,panfengfeng/spark,zhouyejoe/spark,byakuinss/spark,JerryLead/spark,tengpeng/spark,patrick-nicholson/spark,jrshust/spark,adrian-ionescu/apache-spark,WeichenXu123/spark,shubhamchopra/spark,setjet/spark,hvanhovell/spark,stanzhai/spark,kissmetrics/spark,gioenn/xSpark,mahak/spark,metamx/spark,janewangfb/spark,JerryLead/spark,lvdongr/spark,skonto/spark,dhruve/spark,saturday-shi/spark,yanboliang/spark,adrian-ionescu/apache-spark,huang1900/spark,apache-spark-on-k8s/spark,nchammas/spark,ahnqirage/spark,jlopezmalla/spark,ptkool/spark,LantaoJin/spark,ddna1021/spark,liyichao/spark,bravo-zhang/spark,vinodkc/spark,dongjoon-hyun/spark,mahak/spark,bravo-zhang/spark,dhruve/spark,poffuomo/spark,jlopezmalla/spark,ibm-research-ireland/sparkoscope,cloud-fan/spark,WindCanDie/spark,milliman/spark,matthewfranglen/spark,nlalevee/spark,andrewor14/spark,ahnqirage/spark,WindCanDie/spark,1haodian/spark,xflin/spark,taroplus/spark,huang1900/spark,skonto/spark,pgandhi999/spark,metamx/spark,1haodian/spark,brad-kaiser/spark,map222/spark,ahnqirage/spark,loneknightpy/spark,byakuinss/spark,aray/spark,srowen/spark,esi-mineset/spark,Aegeaner/spark,SnappyDataInc/spark,tengpeng/spark,joseph-torres/spark,jiangxb1987/spark,narahari92/spark,caneGuy/spark,rekhajoshm/spark,haowu80s/spark,eyalfa/spark,mike0sv/spark,minixalpha/spark,sachintyagi22/spark,hhbyyh/spark,bOOm-X/spark,wangyum/spark,UndeadBaneGitHub/spark,maropu/spark,Panos-Bletsos/spark-cost-model-optimizer,ajaysaini725/spark,Panos-Bletsos/spark-cost-model-optimizer,wangyum/spark,nilsgrabbert/spark,liutang123/spark,eyalfa/spark,icexelloss/spark,shubhamchopra/spark,HyukjinKwon/spark,nilsgrabbert/spark,stanzhai/spark,chuckchen/spark,LantaoJin/spark,shaneknapp/spark,saturday-shi/spark,cin/spark,someorz/spark,aosagie/spark,saltstar/spark,ioana-delaney/spark,SHASHANKB/spark,narahari92/spark,brad-kaiser/spark,wangyum/spark,lxsmnv/spark,zero323/spark,shaneknapp/spark,JerryLead/spark,aray/spark,setjet/spark,jianran/spark,dbtsai/spark,lxsmnv/spark,jkbradley/spark,dongjoon-hyun/spark,bdrillard/spark,cin/spark,jkbradley/spark,publicRoman/spark,sureshthalamati/spark,srowen/spark,rikima/spark,ueshin/apache-spark,nchammas/spark,milliman/spark,metamx/spark,bOOm-X/spark,xflin/spark,mzl9039/spark,HyukjinKwon/spark,skonto/spark,pronix/spark,ericvandenbergfb/spark,publicRoman/spark,highfei2011/spark,cin/spark,spark-test/spark,maropu/spark,dongjoon-hyun/spark,icexelloss/spark,eyalfa/spark,debugger87/spark,yanboliang/spark,zero323/spark,sahilTakiar/spark,andrewor14/iolap,gengliangwang/spark,ibm-research-ireland/sparkoscope,wangmiao1981/spark,markhamstra/spark,mike0sv/spark,rednaxelafx/apache-spark,Panos-Bletsos/spark-cost-model-optimizer,1haodian/spark,pronix/spark,shuangshuangwang/spark,joseph-torres/spark,debugger87/spark,hvanhovell/spark,kevinyu98/spark,1haodian/spark,mzl9039/spark,mdespriee/spark,liutang123/spark,jrshust/spark,WindCanDie/spark,stanzhai/spark,ueshin/apache-spark,kiszk/spark,xflin/spark,ron8hu/spark,nlalevee/spark,byakuinss/spark,actuaryzhang/spark,map222/spark,markhamstra/spark,ptkool/spark,BryanCutler/spark,esi-mineset/spark,tengpeng/spark,srowen/spark,saltstar/spark,pgandhi999/spark,saltstar/spark,facaiy/spark,saturday-shi/spark,adrian-ionescu/apache-spark,alunarbeach/spark,gengliangwang/spark,bravo-zhang/spark,minixalpha/spark,skonto/spark,nlalevee/spark,mahak/spark,tengpeng/spark,kimoonkim/spark,rezasafi/spark,MLnick/spark,vinodkc/spark,eyalfa/spark,bravo-zhang/spark,apache/spark,ron8hu/spark,loneknightpy/spark,stanzhai/spark,akopich/spark,kissmetrics/spark,zero323/spark,zuotingbing/spark,ahnqirage/spark,kiszk/spark,sahilTakiar/spark,1haodian/spark,shubhamchopra/spark,sachintyagi22/spark,mdespriee/spark,cloud-fan/spark,ConeyLiu/spark,sachintyagi22/spark,xuanyuanking/spark,kimoonkim/spark,esi-mineset/spark