Under a multi-region deployment with a single Keystone server,
specifying the Keystone auth credentials isn't enough. Indeed,
Castellan succeeds when logging-in, but may use the wrong
Barbican endpoint (if there are 2 Barbican deployed). This is
what happened to us, when deploying our 2nd region.
They way to fix it would be to tell Castellan what region to use,
unfortunately, there's no such option in Castellan. Though we may
specify the barbican_endpoint, which is what this patch allows.
Change-Id: Ib7f4219ef5fdef65e9cfd5701e28b5288741783e
90da23c7d2