Implement secure RBAC for share instances
Implement secure RBAC for share instances

This commit updates the policies for share instances 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: I1978fd95f5a9f798dd2d5a2ca011952515319746

openstack/manila,openstack/manila