sst_dump: Add --output_hex option and output the same format as ldb dump
sst_dump: Add --output_hex option and output the same format as ldb dump

Summary: Now sst_dump has the same option --output_hex as "ldb dump" and also share the same output format.  So we can do "sst_dump ... | ldb load ..." for an experiment.

Test Plan:
[zshao@dev485 ~/git/rocksdb] ./sst_dump --file=/data/users/zshao/test_leveldb/000005.sst  --output_hex | head -n 2
0000027F4FBE00000101000000000000 ==> D901000000000000000057596F7520726563656976656420746F6461792773207370656369616C20676966742120436C69636B2041636365707420746F207669657720796F75722047696674206265666F72652069742064697361707065617273210000000000000000
000007F9C2D400000102000000000000 ==> 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

Reviewers: dhruba, sheki, emayanke

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D7587

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