Add 'datasource: influxdb' to Grafana meta

Change-Id: Ia10be76a6e17259e4c5ebbe70eaedd04dd43bb2d
diff --git a/kubernetes/meta/grafana.yml b/kubernetes/meta/grafana.yml
index a6c46ba..3d653e3 100644
--- a/kubernetes/meta/grafana.yml
+++ b/kubernetes/meta/grafana.yml
@@ -31,6 +31,7 @@
     template: kubernetes/files/grafana_dashboards/calico_influxdb.json
 {%- endif %}
   main:
+    datasource: influxdb
     row:
       kubernetes-control-plane:
         title: Kubernetes Control Plane