Summary:
format_version=5 enables new Bloom filter. Using 2/5
probability for "latest and greatest" rather than naive 1/4.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6102

Test Plan: start 'make blackbox_crash_test'

Differential Revision: D18735685

Pulled By: pdillinger

fbshipit-source-id: e81529c8a3f53560d246086ee5f92ee7d79a2eab