Add 'datasource: influxdb' to Grafana meta

Change-Id: I18902bcd35fccab1422f07f9d419cd99b6ebbf8b
diff --git a/etcd/meta/grafana.yml b/etcd/meta/grafana.yml
index 9007964..fecdf6d 100644
--- a/etcd/meta/grafana.yml
+++ b/etcd/meta/grafana.yml
@@ -10,6 +10,7 @@
     format: json
     template: etcd/files/grafana_dashboards/etcd_influxdb.json
   main:
+    datasource: influxdb
     row:
       etcd-control-plane:
         title: Etcd Cluster