Implement secure RBAC for share networks
Implement secure RBAC for share networks

This commit updates the policies for share networks 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: Ie5e87c73e97d4a464ec91db8fba1c5d3e9abfff5

openstack/manila,openstack/manila