permission plugin: Auto-add operational atttributes to read permissions
    
    The attributes entryusn, createtimestamp, and modifytimestamp
    should be readable whenever thir entry is, i.e. when we allow reading
    the objectclass.
    Automatically add them to every read permission that includes objectclass.
    
    https://fedorahosted.org/freeipa/ticket/4534
    
    Reviewed-By: Martin Kosek <mkosek@redhat.com>