Add 'readtocache' test
Add 'readtocache' test

Summary:
For some tests I want to cache the database prior to running other tests on the same invocation
of db_bench. The readtocache test ignores --threads and --reads so those can be used by other tests
and it will still do a full read of --num rows with one thread. It might be invoked like:
  db_bench --benchmarks=readtocache,readrandom --reads 100 --num 10000 --threads 8

Task ID: #

Blame Rev:

Test Plan:
run db_bench

Revert Plan:

Database Impact:

Memcache Impact:

Other Notes:

EImportant:

- begin *PUBLIC* platform impact section -
Bugzilla: #
- end platform impact -

Reviewers: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14739

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/rocksdb,caijieming-baidu/rocksdb,vmx/rocksdb,alihalabyah/rocksdb,hobinyoon/rocksdb,SunguckLee/RocksDB,ylong/rocksdb,biddyweb/rocksdb,wskplho/rocksdb,NickCis/rocksdb,vashstorm/rocksdb,siddhartharay007/rocksdb,biddyweb/rocksdb,lgscofield/rocksdb,wenduo/rocksdb,JoeWoo/rocksdb,RyanTech/rocksdb,caijieming-baidu/rocksdb,hobinyoon/rocksdb,RyanTech/rocksdb,kaschaeffer/rocksdb,geraldoandradee/rocksdb,OverlordQ/rocksdb,anagav/rocksdb,Applied-Duality/rocksdb,alihalabyah/rocksdb,zhangpng/rocksdb,dkorolev/rocksdb,siddhartharay007/rocksdb,facebook/rocksdb,vmx/rocksdb,temicai/rocksdb,Andymic/rocksdb,geraldoandradee/rocksdb,luckywhu/rocksdb,Vaisman/rocksdb,norton/rocksdb,RyanTech/rocksdb,wlqGit/rocksdb,wskplho/rocksdb,amyvmiwei/rocksdb,ryneli/rocksdb,lgscofield/rocksdb,tschottdorf/rocksdb,amyvmiwei/rocksdb,facebook/rocksdb,alihalabyah/rocksdb,luckywhu/rocksdb,temicai/rocksdb,dkorolev/rocksdb,bbiao/rocksdb,wenduo/rocksdb,bbiao/rocksdb,fengshao0907/rocksdb,JoeWoo/rocksdb,JackLian/rocksdb,wat-ze-hex/rocksdb,Andymic/rocksdb,siddhartharay007/rocksdb,flabby/rocksdb,wlqGit/rocksdb,flabby/rocksdb,RyanTech/rocksdb,kaschaeffer/rocksdb,facebook/rocksdb,bbiao/rocksdb,Applied-Duality/rocksdb,virtdb/rocksdb,anagav/rocksdb,tschottdorf/rocksdb,Andymic/rocksdb,tschottdorf/rocksdb,SunguckLee/RocksDB,msb-at-yahoo/rocksdb