Keystone RPC backend config consistency

lib/keystone was setting up rabbit config directly rather than
using the iniset_rpc_backend function that other projects use.

Change-Id: Ic368f102c808cdbd2e4cbc1ff457cdf17a681332
diff --git a/lib/keystone b/lib/keystone
index 0968445..c9433d9 100644
--- a/lib/keystone
+++ b/lib/keystone
@@ -226,12 +226,7 @@
         iniset $KEYSTONE_CONF assignment driver "keystone.assignment.backends.$KEYSTONE_ASSIGNMENT_BACKEND.Assignment"
     fi
 
-    # Configure rabbitmq credentials
-    if is_service_enabled rabbit; then
-        iniset $KEYSTONE_CONF DEFAULT rabbit_userid $RABBIT_USERID
-        iniset $KEYSTONE_CONF DEFAULT rabbit_password $RABBIT_PASSWORD
-        iniset $KEYSTONE_CONF DEFAULT rabbit_host $RABBIT_HOST
-    fi
+    iniset_rpc_backend keystone $KEYSTONE_CONF DEFAULT
 
     # Set the URL advertised in the ``versions`` structure returned by the '/' route
     if is_service_enabled tls-proxy; then