Make DBTest.ReadLatencyHistogramByLevel more robust
Make DBTest.ReadLatencyHistogramByLevel more robust

Summary: DBTest.ReadLatencyHistogramByLevel was not written as expected. After writes, reads aren't guaranteed to hit data written. It was not expected. Fix it.

Test Plan: Run the test multiple times

Reviewers: IslamAbdelRahman, rven, anthony, kradhakrishnan, yhchiang, igor

Reviewed By: igor

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D46587

JackLian/rocksdb,JoeWoo/rocksdb,SunguckLee/RocksDB,flabby/rocksdb,vmx/rocksdb,RyanTech/rocksdb,OverlordQ/rocksdb,vmx/rocksdb,JackLian/rocksdb,Vaisman/rocksdb,luckywhu/rocksdb,luckywhu/rocksdb,wenduo/rocksdb,Vaisman/rocksdb,Vaisman/rocksdb,SunguckLee/RocksDB,vmx/rocksdb,JackLian/rocksdb,facebook/rocksdb,geraldoandradee/rocksdb,norton/rocksdb,vmx/rocksdb,JoeWoo/rocksdb,geraldoandradee/rocksdb,caijieming-baidu/rocksdb,JohnPJenkins/rocksdb,wat-ze-hex/rocksdb,tsheasha/rocksdb,JoeWoo/rocksdb,luckywhu/rocksdb,SunguckLee/RocksDB,vmx/rocksdb,JoeWoo/rocksdb,biddyweb/rocksdb,caijieming-baidu/rocksdb,norton/rocksdb,kaschaeffer/rocksdb,wenduo/rocksdb,RyanTech/rocksdb,luckywhu/rocksdb,OverlordQ/rocksdb,bbiao/rocksdb,JackLian/rocksdb,vmx/rocksdb,RyanTech/rocksdb,ryneli/rocksdb,wat-ze-hex/rocksdb,wenduo/rocksdb,hobinyoon/rocksdb,kaschaeffer/rocksdb,caijieming-baidu/rocksdb,JohnPJenkins/rocksdb,wenduo/rocksdb,facebook/rocksdb,OverlordQ/rocksdb,facebook/rocksdb,facebook/rocksdb,flabby/rocksdb,vmx/rocksdb,norton/rocksdb,biddyweb/rocksdb,luckywhu/rocksdb,facebook/rocksdb,JohnPJenkins/rocksdb,norton/rocksdb,kaschaeffer/rocksdb,Andymic/rocksdb,Vaisman/rocksdb,jalexanderqed/rocksdb,JackLian/rocksdb,OverlordQ/rocksdb,tsheasha/rocksdb,norton/rocksdb,geraldoandradee/rocksdb,kaschaeffer/rocksdb,RyanTech/rocksdb,jalexanderqed/rocksdb,tsheasha/rocksdb,Andymic/rocksdb,jalexanderqed/rocksdb,Vaisman/rocksdb,bbiao/rocksdb,luckywhu/rocksdb,JohnPJenkins/rocksdb,JoeWoo/rocksdb,flabby/rocksdb,JohnPJenkins/rocksdb,bbiao/rocksdb,wat-ze-hex/rocksdb,kaschaeffer/rocksdb,wat-ze-hex/rocksdb,biddyweb/rocksdb,biddyweb/rocksdb,ryneli/rocksdb,jalexanderqed/rocksdb,wenduo/rocksdb,tsheasha/rocksdb,OverlordQ/rocksdb,RyanTech/rocksdb,jalexanderqed/rocksdb,kaschaeffer/rocksdb,hobinyoon/rocksdb,geraldoandradee/rocksdb,JoeWoo/rocksdb,hobinyoon/rocksdb,norton/rocksdb,Andymic/rocksdb,geraldoandradee/rocksdb,facebook/rocksdb,JohnPJenkins/rocksdb,jalexanderqed/rocksdb,wenduo/rocksdb,tsheasha/rocksdb,wenduo/rocksdb,JackLian/rocksdb,Andymic/rocksdb,flabby/rocksdb,jalexanderqed/rocksdb,Vaisman/rocksdb,OverlordQ/rocksdb,wat-ze-hex/rocksdb,caijieming-baidu/rocksdb,wat-ze-hex/rocksdb,wat-ze-hex/rocksdb,kaschaeffer/rocksdb,caijieming-baidu/rocksdb,wenduo/rocksdb,RyanTech/rocksdb,tsheasha/rocksdb,flabby/rocksdb,Andymic/rocksdb,biddyweb/rocksdb,facebook/rocksdb,bbiao/rocksdb,flabby/rocksdb,ryneli/rocksdb,ryneli/rocksdb,JackLian/rocksdb,vmx/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,SunguckLee/RocksDB,hobinyoon/rocksdb,ryneli/rocksdb,hobinyoon/rocksdb,Andymic/rocksdb,bbiao/rocksdb,tsheasha/rocksdb,OverlordQ/rocksdb,SunguckLee/RocksDB,Vaisman/rocksdb,flabby/rocksdb,caijieming-baidu/rocksdb,Andymic/rocksdb,hobinyoon/rocksdb,caijieming-baidu/rocksdb,wat-ze-hex/rocksdb,hobinyoon/rocksdb,Andymic/rocksdb,norton/rocksdb,norton/rocksdb,biddyweb/rocksdb,geraldoandradee/rocksdb,ryneli/rocksdb,RyanTech/rocksdb,tsheasha/rocksdb,JohnPJenkins/rocksdb,SunguckLee/RocksDB,SunguckLee/RocksDB,biddyweb/rocksdb,facebook/rocksdb,JoeWoo/rocksdb,luckywhu/rocksdb,geraldoandradee/rocksdb,hobinyoon/rocksdb,bbiao/rocksdb,bbiao/rocksdb,ryneli/rocksdb