Fix endpoint error when running keystone on apache

When running keystone in httpd, horizon could not generate the
right keystone endpoint url. Fixes this issue by retrieving the
whole path from the service_catalog or OPENSTACK_KEYSTONE_URL
and generating a new url.

Change-Id: Id8459947498127e47700d9f690d4ed4d5cadbba9
Closes-bug: #1295128
Merge "Fix endpoint error when running keystone on apache"