build db every monday
build db every monday

Summary:
Rebuilding regression db at the first run every monday.
Closes https://github.com/facebook/rocksdb/pull/2093

Differential Revision: D4836961

Pulled By: lightmark

fbshipit-source-id: 22d6c25

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