Add Barbican Wrapper Specification

Previously approved spec in Juno: https://review.openstack.org/#/c/94918/
Code requiring this spec is here: https://review.openstack.org/#/c/104001

Previously-approved: juno

Change-Id: I348152f35395b8ef63ac947c58d5aa15b3afdd41
Merge "Add Barbican Wrapper Specification"