This patch introduces the user-meta database table, model, and
repository. It is the first of several patches which will complete
the "User Defined Metadata for Barbican Secrets" Blueprint.
Other Patches will include:
1. ) API and Tests(Unit and Functional)
2. ) Documentation
3. ) Client Upgrades
Implements: blueprint add-user-metadata
Change-Id: I4b6ae9e7090eb66fe8c89e62116d9a8483642a29