Summary:
1. DBImplReadOnly::GetLiveFiles should not return NotSupported. Instead, it
   should call DBImpl::GetLiveFiles(flush_memtable=false).
2. In DBImp::Recover, we should also recover the OPTIONS file name and/or
   number so that an immediate subsequent GetLiveFiles will get the correct
   OPTIONS name.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4681

Differential Revision: D13069205

Pulled By: riversand963

fbshipit-source-id: 3e6a0174307d06db5a01feb099b306cea1f7f88a