Add 'datasource: influxdb' to Grafana meta

Change-Id: I4aedfc40b97ea642759edd9c74f54a5b026f8cda
diff --git a/memcached/meta/grafana.yml b/memcached/meta/grafana.yml
index 7e18807..56bebfe 100644
--- a/memcached/meta/grafana.yml
+++ b/memcached/meta/grafana.yml
@@ -8,6 +8,7 @@
     format: json
     template: memcached/files/grafana_dashboards/memcached_influxdb.json
   main:
+    datasource: influxdb
     row:
       ost-middleware:
         title: Middleware