First attempt to integrate Paul's HSM plugin into Barbican.

Initial mods to change the plugin interface a little bit, and to introduce
a new 'kek_data' table to house key encryption key (KEK) metadata used for
encryption/decryption. This new table will house per-tenant metadata.

Change-Id: I87cd0d4516fa19209be94cacdb79ac4b7eb740df
Implements: blueprint crypto-implement-hsm-plugin