TT#26264 Check for empty grafana.db

Grafana will consider the database to be R/O if it's an empty file, and
refuse to start. Check for this condition.

Change-Id: Iad2f1ed4fb03370432d438c4dcd3bab342ac2588
(cherry picked from commit c0639f36b6)

templates/911_service-grafana.yaml.tt2

@@ -12,6 +12,14 @@
   is_li_enabled = is_li && cluster_sets.type == 'distributed' && intercept.enable == 'yes';
 -%]
 
+file:
+
+  /var/lib/grafana/grafana.db:
+    exists: true
+    filetype: file
+    size:
+      not: 0
+
 command:
 
 [% IF grafana.enable == 'yes' && (is_mgmt || is_li_enabled) -%]