Originally there was only the secret for authentication so we didn't use
any suffix to tell it apart. With the introduction of encryption we
added a 'luks' suffix for the encryption secrets. Since encryption is
really generic and authentication is not the only secret modify the
aliases for the secrets to better describe what they are used for.

This is possible as we store the disk secrets in the status XML thus
only new machines will use the new secrets.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>