[CF] Flush all memtables on column family drop
[CF] Flush all memtables on column family drop

Summary: When column family is dropped, we want to delete all WALs that refer to it. To do that, we need to make them obsolete by flushing all the memtables

Test Plan: column_family_test

Reviewers: dhruba, haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16557

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