Summary:
The db_bench test was not using the specified value for the max-file-open. Fixed.
The fs readhead is switched off.
Gather statistics about the table cache and print it out at the end of the tets run.
Test Plan: Revert Plan:
Reviewers: adsharma, sc
Reviewed By: adsharma
Differential Revision: https://reviews.facebook.net/D3441
