db_bench to by default verify checksum
db_bench to by default verify checksum

Summary: Closes https://github.com/facebook/rocksdb/pull/2575

Differential Revision: D5417350

Pulled By: siying

fbshipit-source-id: 4bc11e35a7256167a5a7d2f586f2ac74c0deddb0

Andymic/rocksdb,Andymic/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,bbiao/rocksdb,Andymic/rocksdb,bbiao/rocksdb,Andymic/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,SunguckLee/RocksDB,bbiao/rocksdb,SunguckLee/RocksDB,Andymic/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,bbiao/rocksdb,Andymic/rocksdb,bbiao/rocksdb