Add missing JSON format for dashboard

Change-Id: Ibb3ea64049e809a17d57aaae420a4966c4c986b6
diff --git a/glance/meta/grafana.yml b/glance/meta/grafana.yml
index f9a0646..7a0a735 100644
--- a/glance/meta/grafana.yml
+++ b/glance/meta/grafana.yml
@@ -1,3 +1,4 @@
 dashboard:
   glance:
+    format: json
     template: glance/files/grafana_influxdb.json