Summary:
https://github.com/facebook/rocksdb/pull/4960 introduced ignorable manfiest
record. Adding a test to it.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4964

Differential Revision: D14012667

Pulled By: siying

fbshipit-source-id: e5f10ecc68dec2716e178d44f0fe2b76c3d857ef