[SPARK-19604][TESTS] Log the start of every Python test
[SPARK-19604][TESTS] Log the start of every Python test

## What changes were proposed in this pull request?
Right now, we only have info level log after we finish the tests of a Python test file. We should also log the start of a test. So, if a test is hanging, we can tell which test file is running.

## How was this patch tested?
This is a change for python tests.

Author: Yin Huai <yhuai@databricks.com>

Closes #16935 from yhuai/SPARK-19604.

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