Summary:
- When options file is provided to db_stress, take supported options from the file instead of from flags
- Call `BuildOptionsTable` after `Open` so it can use `options_` once it has been populated either from flags or from file
- Allow options filename to be passed via `db_crashtest.py`
Closes https://github.com/facebook/rocksdb/pull/3768
Differential Revision: D7755331
Pulled By: ajkr
fbshipit-source-id: 5205cc5deb0d74d677b9832174153812bab9a60a