Barbican returns ref not uuid

[yuanying]

We decided to use barbican to store certs and that uuid is stored in bay model.
But Barbican doesn't return uuid, it returns reference (uri),
So we should modify db table to store uri.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/218086

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/218086
Committed: https://git.openstack.org/cgit/openstack/magnum/commit/?id=7a51a250f6f36e549c231f868430257e401a4ed8
Submitter: Jenkins
Branch: master

commit 7a51a250f6f36e549c231f868430257e401a4ed8
Author: OTSUKA, Yuanying <email address hidden>
Date: Fri Aug 28 13:27:48 2015 +0900

    Change bay.*_cert_uuid to bay.*_cert_ref

    We decided to use barbican to store certs, and uuid of certs are
    stored to bay. But Barbican doesn't return uuid, it returns URI. So
    we should modify db table to store uri.

    Change-Id: I5c6baf43b35df9a1134fce4fbc581d7642fa8e84
    Closes-Bug: #1489707
    Partial-Implements: blueprint magnum-as-a-ca