Policy.json should be defined by user

User can override and add values to policy.json by creating flat
key-value structure under ceilometer:server:policy.

Change-Id: Ifeb2dbf54b0e32eb10a58f853a05fabf930a55a4
diff --git a/metadata.yml b/metadata.yml
index ee39cb8..7f502d1 100644
--- a/metadata.yml
+++ b/metadata.yml
@@ -1,3 +1,6 @@
 name: "ceilometer"
 version: "2016.4.1"
 source: "https://github.com/openstack/salt-formula-ceilometer"
+dependencies:
+  - name: keystone
+    source: "https://github.com/salt-formulas/salt-formula-keystone"