calculate endpoint URLs more consistently

To clarify the various endpoint URLs in use, it makes sense for
them to be calculated in the same place, and in a consistent manner.
Introducing helper methods facilitates this.
add HA support via pacemaker barclamp

Allow the keystone-server role to be applied to more than one node.  If
HA mode is enabled, virtual IPs are allocated on the admin and public
networks, and grouped together with a Pacemaker resource primitive which
controls the keystone server service.