Add 'datasource: influxdb' to Grafana meta

Change-Id: I735a9cf2579241c3261912147d67df5302e7f5cf
diff --git a/cinder/meta/grafana.yml b/cinder/meta/grafana.yml
index c43f5f8..3d30b8c 100644
--- a/cinder/meta/grafana.yml
+++ b/cinder/meta/grafana.yml
@@ -8,6 +8,7 @@
     format: json
     template: cinder/files/grafana_dashboards/cinder_influxdb.json
   service_level:
+    datasource: influxdb
     row:
       cinder-service-level:
         title: Cinder Service Levels
@@ -69,6 +70,7 @@
                 rawQuery: true
                 query: SELECT count(max) FROM openstack_cinder_http_response_times WHERE environment_label = '$environment' AND http_status = '5xx' AND $timeFilter
   main:
+    datasource: influxdb
     row:
       ost-control-plane:
         title: OpenStack Control Plane