Description of problem: Any permissions in MDS caps besides "allow *" and "allow w" must start with "allow r" or "allow rw". Otherwise the MDS cap is rejected. The error printed by MDS in this case is the generic error the MDS prints in every case of incorrect MDS caps. Unlike some other Ceph daemons, MDS doesn't permission like "allow w". Therefore, print a special error message so that users are specifically told that the permissions in the MDS caps, besides "all" and "*", must start with "r" or "rw". Such a message is printed in case of "ceph fs authorize" but the commands "ceph auth add", "ceph auth caps", "ceph auth get-or-create" and "ceph auth get-or-create-key" don't. Let's make these commands too print a special message. Version-Release number of selected component (if applicable): How reproducible: Everytime