Add missing JSON format for dashboard

Change-Id: If85b68337760941f5fb528898a739e6828203e46
diff --git a/nova/meta/grafana.yml b/nova/meta/grafana.yml
index 665963f..421260c 100644
--- a/nova/meta/grafana.yml
+++ b/nova/meta/grafana.yml
@@ -1,3 +1,4 @@
 dashboard:
   nova:
+    format: json
     template: nova/files/grafana_influxdb.json