Fixed signed-unsigned comparison warning in db_test.cc
Fixed signed-unsigned comparison warning in db_test.cc

Summary:
Fixed signed-unsigned comparison warning in db_test.cc

db/db_test.cc:8606:3: note: in instantiation of function template specialization 'rocksdb::test::Tester::IsEq<int, unsigned long>' requested here
  ASSERT_EQ(2, metadata.size());
    ^

Test Plan:
make db_test

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