[magnum] Remove trusty regex for stable/mitaka
[magnum] Remove trusty regex for stable/mitaka

Trusty jobs are caught by a global regex.

Also, remove the identity-v3-only job running on trusty.

Change-Id: I3a928a482e885b26f59400f7b92a18115cef60a0

openstack-infra/project-config,openstack-infra/project-config