enable plain table in db_bench
enable plain table in db_bench

Summary: as title

Test Plan: ran db_bench to gather stats

Reviewers: haobo, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16059

SunguckLee/RocksDB,wskplho/rocksdb,fengshao0907/rocksdb,msb-at-yahoo/rocksdb,JackLian/rocksdb,sorphi/rocksdb,tschottdorf/rocksdb,OverlordQ/rocksdb,luckywhu/rocksdb,ylong/rocksdb,virtdb/rocksdb,bbiao/rocksdb,IMCG/RcoksDB,facebook/rocksdb,JohnPJenkins/rocksdb,alihalabyah/rocksdb,dkorolev/rocksdb,Applied-Duality/rocksdb,JoeWoo/rocksdb,wlqGit/rocksdb,geraldoandradee/rocksdb,kaschaeffer/rocksdb,sorphi/rocksdb,hobinyoon/rocksdb,JoeWoo/rocksdb,JoeWoo/rocksdb,JoeWoo/rocksdb,hobinyoon/rocksdb,makelivedotnet/rocksdb,rDSN-Projects/rocksdb.replicated,wenduo/rocksdb,JohnPJenkins/rocksdb,tschottdorf/rocksdb,tschottdorf/rocksdb,facebook/rocksdb,anagav/rocksdb,msb-at-yahoo/rocksdb,biddyweb/rocksdb,jalexanderqed/rocksdb,JackLian/rocksdb,hobinyoon/rocksdb,flabby/rocksdb,amyvmiwei/rocksdb,Andymic/rocksdb,geraldoandradee/rocksdb,ylong/rocksdb,tsheasha/rocksdb,temicai/rocksdb,caijieming-baidu/rocksdb,amyvmiwei/rocksdb,hobinyoon/rocksdb,luckywhu/rocksdb,caijieming-baidu/rocksdb,Andymic/rocksdb,facebook/rocksdb,wat-ze-hex/rocksdb,amyvmiwei/rocksdb,wlqGit/rocksdb,anagav/rocksdb,wenduo/rocksdb,NickCis/rocksdb,SunguckLee/RocksDB,JackLian/rocksdb,OverlordQ/rocksdb,ylong/rocksdb,fengshao0907/rocksdb,RyanTech/rocksdb,wskplho/rocksdb,lgscofield/rocksdb,biddyweb/rocksdb,Applied-Duality/rocksdb,OverlordQ/rocksdb,facebook/rocksdb,tizzybec/rocksdb,bbiao/rocksdb,tsheasha/rocksdb,ryneli/rocksdb,fengshao0907/rocksdb,ryneli/rocksdb,luckywhu/rocksdb,temicai/rocksdb,vashstorm/rocksdb,sorphi/rocksdb,facebook/rocksdb,mbarbon/rocksdb,norton/rocksdb,IMCG/RcoksDB,wenduo/rocksdb,Andymic/rocksdb,norton/rocksdb,wskplho/rocksdb,SunguckLee/RocksDB,lgscofield/rocksdb,NickCis/rocksdb,RyanTech/rocksdb,amyvmiwei/rocksdb,sorphi/rocksdb,JohnPJenkins/rocksdb,RyanTech/rocksdb,wat-ze-hex/rocksdb,vmx/rocksdb,vmx/rocksdb,Vaisman/rocksdb,norton/rocksdb,bbiao/rocksdb,makelivedotnet/rocksdb,ylong/rocksdb,kaschaeffer/rocksdb,Applied-Duality/rocksdb,norton/rocksdb,dkorolev/rocksdb,skunkwerks/rocksdb,tsheasha/rocksdb,flabby/rocksdb,flabby/rocksdb,temicai/rocksdb,geraldoandradee/rocksdb,anagav/rocksdb,mbarbon/rocksdb,tschottdorf/rocksdb,makelivedotnet/rocksdb,temicai/rocksdb,flabby/rocksdb,biddyweb/rocksdb,jalexanderqed/rocksdb,siddhartharay007/rocksdb,Andymic/rocksdb,zhangpng/rocksdb,vashstorm/rocksdb,wenduo/rocksdb,vmx/rocksdb,kaschaeffer/rocksdb,wlqGit/rocksdb,mbarbon/rocksdb,vmx/rocksdb,wenduo/rocksdb,hobinyoon/rocksdb,SunguckLee/RocksDB,temicai/rocksdb,alihalabyah/rocksdb,bbiao/rocksdb,JackLian/rocksdb,wlqGit/rocksdb,tizzybec/rocksdb,zhangpng/rocksdb,Applied-Duality/rocksdb,temicai/rocksdb,NickCis/rocksdb,SunguckLee/RocksDB,jalexanderqed/rocksdb,wat-ze-hex/rocksdb,skunkwerks/rocksdb,Applied-Duality/rocksdb,wenduo/rocksdb,msb-at-yahoo/rocksdb,caijieming-baidu/rocksdb,Vaisman/rocksdb,caijieming-baidu/rocksdb,JackLian/rocksdb,alihalabyah/rocksdb,siddhartharay007/rocksdb,IMCG/RcoksDB,tsheasha/rocksdb,zhangpng/rocksdb,tsheasha/rocksdb,IMCG/RcoksDB,fengshao0907/rocksdb,OverlordQ/rocksdb,caijieming-baidu/rocksdb,caijieming-baidu/rocksdb,IMCG/RcoksDB,vmx/rocksdb,luckywhu/rocksdb,makelivedotnet/rocksdb,rDSN-Projects/rocksdb.replicated,ryneli/rocksdb,virtdb/rocksdb,biddyweb/rocksdb,JohnPJenkins/rocksdb,virtdb/rocksdb,flabby/rocksdb,ryneli/rocksdb,siddhartharay007/rocksdb,anagav/rocksdb,anagav/rocksdb,wat-ze-hex/rocksdb,Andymic/rocksdb,JoeWoo/rocksdb,tsheasha/rocksdb,norton/rocksdb,IMCG/RcoksDB,makelivedotnet/rocksdb,sorphi/rocksdb,SunguckLee/RocksDB,Vaisman/rocksdb,hobinyoon/rocksdb,mbarbon/rocksdb,rDSN-Projects/rocksdb.replicated,flabby/rocksdb,NickCis/rocksdb,NickCis/rocksdb,facebook/rocksdb,vashstorm/rocksdb,dkorolev/rocksdb,ylong/rocksdb,mbarbon/rocksdb,Vaisman/rocksdb,norton/rocksdb,caijieming-baidu/rocksdb,sorphi/rocksdb,siddhartharay007/rocksdb,dkorolev/rocksdb,mbarbon/rocksdb,Andymic/rocksdb,Vaisman/rocksdb,OverlordQ/rocksdb,geraldoandradee/rocksdb,ryneli/rocksdb,flabby/rocksdb,OverlordQ/rocksdb,Andymic/rocksdb,biddyweb/rocksdb,biddyweb/rocksdb,dkorolev/rocksdb,RyanTech/rocksdb,virtdb/rocksdb,skunkwerks/rocksdb,virtdb/rocksdb,wskplho/rocksdb,lgscofield/rocksdb,zhangpng/rocksdb,amyvmiwei/rocksdb,jalexanderqed/rocksdb,hobinyoon/rocksdb,lgscofield/rocksdb,tizzybec/rocksdb,kaschaeffer/rocksdb,kaschaeffer/rocksdb,rDSN-Projects/rocksdb.replicated,OverlordQ/rocksdb,tizzybec/rocksdb,makelivedotnet/rocksdb,norton/rocksdb,geraldoandradee/rocksdb,bbiao/rocksdb,rDSN-Projects/rocksdb.replicated,tschottdorf/rocksdb,ylong/rocksdb,wlqGit/rocksdb,jalexanderqed/rocksdb,wskplho/rocksdb,ryneli/rocksdb,msb-at-yahoo/rocksdb,alihalabyah/rocksdb,rDSN-Projects/rocksdb.replicated,temicai/rocksdb,Applied-Duality/rocksdb,JoeWoo/rocksdb,NickCis/rocksdb,skunkwerks/rocksdb,amyvmiwei/rocksdb,SunguckLee/RocksDB,fengshao0907/rocksdb,msb-at-yahoo/rocksdb,jalexanderqed/rocksdb,JohnPJenkins/rocksdb,JackLian/rocksdb,skunkwerks/rocksdb,IMCG/RcoksDB,tizzybec/rocksdb,ryneli/rocksdb,tizzybec/rocksdb,facebook/rocksdb,sorphi/rocksdb,wlqGit/rocksdb,dkorolev/rocksdb,wat-ze-hex/rocksdb,NickCis/rocksdb,jalexanderqed/rocksdb,SunguckLee/RocksDB,biddyweb/rocksdb,luckywhu/rocksdb,vashstorm/rocksdb,wenduo/rocksdb,tsheasha/rocksdb,rDSN-Projects/rocksdb.replicated,vmx/rocksdb,Vaisman/rocksdb,JoeWoo/rocksdb,alihalabyah/rocksdb,JohnPJenkins/rocksdb,Andymic/rocksdb,fengshao0907/rocksdb,bbiao/rocksdb,skunkwerks/rocksdb,siddhartharay007/rocksdb,zhangpng/rocksdb,bbiao/rocksdb,virtdb/rocksdb,zhangpng/rocksdb,ylong/rocksdb,skunkwerks/rocksdb,siddhartharay007/rocksdb,wat-ze-hex/rocksdb,amyvmiwei/rocksdb,lgscofield/rocksdb,anagav/rocksdb,alihalabyah/rocksdb,norton/rocksdb,makelivedotnet/rocksdb,virtdb/rocksdb,JohnPJenkins/rocksdb,RyanTech/rocksdb,mbarbon/rocksdb,lgscofield/rocksdb,tizzybec/rocksdb,geraldoandradee/rocksdb,kaschaeffer/rocksdb,wenduo/rocksdb,dkorolev/rocksdb,zhangpng/rocksdb,kaschaeffer/rocksdb,geraldoandradee/rocksdb,hobinyoon/rocksdb,Vaisman/rocksdb,facebook/rocksdb,luckywhu/rocksdb,wlqGit/rocksdb,wskplho/rocksdb,lgscofield/rocksdb,wat-ze-hex/rocksdb,RyanTech/rocksdb,JackLian/rocksdb,anagav/rocksdb,vashstorm/rocksdb,siddhartharay007/rocksdb,alihalabyah/rocksdb,vmx/rocksdb,bbiao/rocksdb,Applied-Duality/rocksdb,tsheasha/rocksdb,RyanTech/rocksdb,tschottdorf/rocksdb,vmx/rocksdb,wat-ze-hex/rocksdb,fengshao0907/rocksdb,msb-at-yahoo/rocksdb,vashstorm/rocksdb,vashstorm/rocksdb,wskplho/rocksdb,luckywhu/rocksdb