Don't fail if keystone_policy is not available

Change-Id: If0ef2a324962520bbf97d0f4a7db33a3b8897066
diff --git a/keystone/meta/salt.yml b/keystone/meta/salt.yml
index ccd9d91..7eccacc 100644
--- a/keystone/meta/salt.yml
+++ b/keystone/meta/salt.yml
@@ -8,9 +8,11 @@
     priority: 520
 grain:
   keystone:
+    {%- if 'keystone_policy' in salt.keys() %}
     keystone_policy:
       {%- set policy_grains = salt['keystone_policy.rule_list'](path="/etc/keystone/policy.json") %}
       {{ policy_grains|yaml(False)|indent(6) }}
+    {%- endif %}
 
 minion:
   {%- if pillar.get('keystone', {}).get('server') or pillar.get('keystone', {}).get('client') %}