Summary:
Currently crash test covers cases with and without atomic flush, but takes too
long to finish. Therefore it may be a better idea to put crash test with atomic
flush in a separate set of tests.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4945

Differential Revision: D13947548

Pulled By: riversand963

fbshipit-source-id: 177c6de865290fd650b0103408339eaa3f801d8c