Implement secure RBAC for pools
Implement secure RBAC for pools

This commit updates the policies for pools 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: I9dc483d409db23af6c89215654757c913a647087

openstack/designate,openstack/designate,openstack/designate