Add stacklight_notification_topic param to SL OS model

Change-Id: Ib52bbfdee08f733c09cbbbd70911c21bec719067
diff --git a/classes/cluster/sl_os_ovs/stacklight/init.yml b/classes/cluster/sl_os_ovs/stacklight/init.yml
index 3b0c8bc..71b5ff3 100644
--- a/classes/cluster/sl_os_ovs/stacklight/init.yml
+++ b/classes/cluster/sl_os_ovs/stacklight/init.yml
@@ -26,6 +26,7 @@
     heka_elasticsearch_host: ${_param:stacklight_monitor_address}
     elasticsearch_port: 9200
     stacklight_environment: ${_param:cluster_domain}
+    stacklight_notification_topic: stacklight_notifications
   linux:
     network:
       host: