Use new syntax for module snippets in rabbitmq_policy and update changelog

messaging/rabbitmq_policy

@@ -151,6 +151,6 @@ def main():
 
     module.exit_json(changed=changed, name=name, state=state)
 
-# this is magic, see lib/ansible/module_common.py
+# import module snippets
-#<<INCLUDE_ANSIBLE_MODULE_COMMON>>
+from ansible.module_utils.basic import *
 main()