[SPARK-15520][SQL] SparkSession builder in python should also allow overriding confs of existing sessions
[SPARK-15520][SQL] SparkSession builder in python should also allow overriding confs of existing sessions

## What changes were proposed in this pull request?

This fixes the python SparkSession builder to allow setting confs correctly. This was a leftover TODO from https://github.com/apache/spark/pull/13200.

## How was this patch tested?

Python doc tests.

cc andrewor14

Author: Eric Liang <ekl@databricks.com>

Closes #13289 from ericl/spark-15520.

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