Set transport_url in proper keystone config section

The RPC transport_url for keystone was being set in the DEFAULT
section, even though keystone doesn't do anything with it. Instead,
keystone leans on the [oslo_messaging_notification] section from
oslo.messaging to register the transport_url option.

This change sets the transport_url in the proper section instead of
using the DEFAULT section.

Change-Id: I11590d0175da7ea310d5529f2d7c0bf8d7fb25b3

Author: lbragstad

lib/keystone

@@ -217,7 +217,7 @@ function configure_keystone {
     iniset $KEYSTONE_CONF cache backend "dogpile.cache.memcached"
     iniset $KEYSTONE_CONF cache memcache_servers localhost:11211
 
-    iniset_rpc_backend keystone $KEYSTONE_CONF
+    iniset_rpc_backend keystone $KEYSTONE_CONF oslo_messaging_notifications
 
     local service_port=$KEYSTONE_SERVICE_PORT
     local auth_port=$KEYSTONE_AUTH_PORT