Summary:
Move an option necessary for running db_bench on multiple CFs into the general initialization area, so it works with both flag-based init and OPTIONS-based init.
Closes https://github.com/facebook/rocksdb/pull/2675
Differential Revision: D5541378
Pulled By: ajkr
fbshipit-source-id: 169926cb4ae95c17974f744faf7cc794d41e5c0a