Point grafana DS to prometheus-relay

Add prometheus relay docker image address

Change-Id: Id1c7800c31b7e4f25684825ba14c91afc573da0c
diff --git a/classes/cluster/virtual-mcp-ocata-ovs/stacklight/server.yml b/classes/cluster/virtual-mcp-ocata-ovs/stacklight/server.yml
index 3a796b8..fd31ac3 100644
--- a/classes/cluster/virtual-mcp-ocata-ovs/stacklight/server.yml
+++ b/classes/cluster/virtual-mcp-ocata-ovs/stacklight/server.yml
@@ -51,6 +51,7 @@
     docker_image_remote_agent: docker-prod-virtual.docker.mirantis.net/openstack-docker/telegraf:latest
     docker_image_remote_storage_adapter: docker-prod-virtual.docker.mirantis.net/openstack-docker/remote_storage_adapter:latest
     docker_image_remote_collector: docker-prod-virtual.docker.mirantis.net/openstack-docker/heka:latest
+    docker_image_prometheus_relay: docker-prod-virtual.docker.mirantis.net/openstack-docker/prometheus_relay:latest
     docker_image_grafana: grafana/grafana:4.3.2
     influxdb_port: 8086
     influxdb_admin_password: password