Summary:
If an error happens during BlobDBImpl::Open after the base DB has been
opened, we need to destroy the `ColumnFamilyHandle`s returned by `DB::Open`
to prevent an assertion in `ColumnFamilySet`'s destructor from being hit.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6763
Test Plan: Ran `make check` and tested using the BlobDB mode of `db_bench`.
Reviewed By: riversand963
Differential Revision: D21262643
Pulled By: ltamasi
fbshipit-source-id: 60ebc7ab19be66cf37fbe5f6d8957d58470f3d3b