Policy.json should be defined by user

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

Change-Id: I1accd9557cc241a55d5e898b9350b34e078b82a6
diff --git a/metadata.yml b/metadata.yml
index 720f1de..c67081b 100644
--- a/metadata.yml
+++ b/metadata.yml
@@ -1,3 +1,6 @@
 name: "heat"
 version: "2016.4.1"
 source: "https://github.com/openstack/salt-formula-heat"
+dependencies:
+  - name: keystone
+    source: "https://github.com/salt-formulas/salt-formula-keystone"