Implement secure RBAC for messages
Implement secure RBAC for messages

This commit updates the policies for messages to understand scope checking and
account for a read-only role. This is part of a broader series of changes
across OpenStack to provide a consistent RBAC experience and improve security.

Change-Id: I30ae2a1d34fb1dcb438880b1a5b46afea7db8d0d

openstack/manila,openstack/manila