Add oslo.policy namespace

As we have used oslo.policy, so we need to add that in
namespace, as oslo.policy has many settings. This followed
other projects genconfig ways.

Partially-implements: blueprint policy-enforce
Change-Id: I83cce25427b65aad6d26f4ea2d6a48170233a4f3

tox.ini

@@ -45,6 +45,7 @@ commands =
     --namespace oslo.db \
     --namespace oslo.log \
     --namespace oslo.messaging \
+    --namespace oslo.policy \
     --namespace keystonemiddleware.auth_token
 
 [flake8]