authorized_keys_d: prevent adding unsupported names.
authorized_keys_d: prevent adding unsupported names.

The names ".", "..", and those containing /'s can't be supported without
introducing escaping.  In the interests of simplicity, just fail on anything
beginning with a "." or containing "/".

stongo/update-ssh-keys,marineam/update-ssh-keys,stongo/update-ssh-keys,marineam/update-ssh-keys,coreos/update-ssh-keys,stongo/update-ssh-keys,coreos/update-ssh-keys,marineam/update-ssh-keys