Reference keystone URIs rather than building URI

lib/keystone sets KEYSTONE_AUTH_URI and KEYSTONE_SERVICE_URI that
other projects should use rather than building the URL themselves.
This will allow us to more easily drop the port altogether.

Change-Id: I7467aae680215f3045d32a088af2187e1eba8169
diff --git a/lib/horizon b/lib/horizon
index abc1f6d..0517e32 100644
--- a/lib/horizon
+++ b/lib/horizon
@@ -96,7 +96,7 @@
     _horizon_config_set $local_settings "" OPENSTACK_HOST \"${KEYSTONE_SERVICE_HOST}\"
 
     _horizon_config_set $local_settings "" OPENSTACK_API_VERSIONS {\"identity\":3}
-    _horizon_config_set $local_settings "" OPENSTACK_KEYSTONE_URL "\"${KEYSTONE_SERVICE_PROTOCOL}://${KEYSTONE_SERVICE_HOST}:${KEYSTONE_SERVICE_PORT}/v3\""
+    _horizon_config_set $local_settings "" OPENSTACK_KEYSTONE_URL "\"${KEYSTONE_SERVICE_URI}/v3\""
 
     if [ -f $SSL_BUNDLE_FILE ]; then
         _horizon_config_set $local_settings "" OPENSTACK_SSL_CACERT \"${SSL_BUNDLE_FILE}\"