Summary:
When the --try_load_options is used in conjunction with the
--column_family option, ldb incorrectly sets the ColumnFamilyOptions for
that column family to defaults. This PR fixes that by retaining from the
OPTIONS file and applying command line overrides.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7847

Test Plan: Add a unit test in ldb_cmd_test

Reviewed By: ajkr

Differential Revision: D25874720

Pulled By: anand1976

fbshipit-source-id: 04bcf23b55e5a30b5b6a59b0e5cb4faef3da7429