nova-manage: squash oslo_policy debug logging

I don't know when it started but you can see from a modern
usage of nova-manage that oslo_policy debug logging is being
emitted. We don't need that debug information in the console
for nova-manage, so this patch hides it just like we do for
oslo_db.

Change-Id: If1a8e8d473846f2626f5e01210f00ad06916a383
Related-Bug: #1650694

nova/cmd/manage.py

@@ -97,7 +97,7 @@
 
 QUOTAS = quota.QUOTAS
 
-_EXTRA_DEFAULT_LOG_LEVELS = ['oslo_db=INFO']
+_EXTRA_DEFAULT_LOG_LEVELS = ['oslo_db=INFO', 'oslo_policy=INFO']
 
 
 # Decorators for actions