Prevent Access rules from being viewed or manipulated by non-owners

Nova will soon have a feature where manila shares can be mounted onto the compute host and made available to client VMs via VirtIOFS [1]. Nova performs this mount on behalf of a user. The user can see the ACLs on the share that nova has mounted. Client identifiers and access secrets are visible in these ACLs - we need a way to prevent this from happening. Alongside, users must also be prevented from deleting this access rule accidentally.