Per the Keystone Install Guide[1] the admin endpoint is superseded in
favor of a single public endpoint. Although internal goes through the
same instance, we should differentiate for project traffic and OpenStack
service traffic.
[1] https://docs.openstack.org/keystone/queens/install/keystone-install-ubuntu.html#install-and-configure-components
Depends-On: Id74966d9f1279f725bc41c08e434230a7845bbc1
Change-Id: I1adb3066c83aaffe8b22f2f2553f634483371974
Implements: blueprint simplify-identity-endpoint