Add oslo.policy.enforcer entry point

this will allow usage of many oslo.policy scripts, e.g.
to generate current effective policy, or to list redundant polices
defined in policy files.

Change-Id: I1de9b6cc16be2896136c7e99cf150c4b8e4603e9
Closes-Bug: #2004421

designate/policy.py

@@ -106,3 +106,11 @@ def enforce_new_defaults():
     if CONF.get('oslo_policy'):
         return CONF['oslo_policy'].get('enforce_new_defaults', False)
     return False
+
+
+def get_enforcer():
+    # This method is used by oslopolicy CLI scripts in order to generate policy
+    # files from overrides on disk and defaults in code.
+    cfg.CONF([], project='designate')
+    init()
+    return _ENFORCER

setup.cfg

@@ -42,6 +42,9 @@ oslo.config.opts.defaults =
 oslo.policy.policies =
     designate = designate.common.policies:list_rules
 
+oslo.policy.enforcer =
+    designate = designate.policy:get_enforcer
+
 console_scripts =
     designate-rootwrap = oslo_rootwrap.cmd:main
     designate-api = designate.cmd.api:main