'Create default ceph args for executing rbd commands.
If no --conf is provided, rbd will look in the default locations e.g.
/etc/ceph/ceph.conf'

def _ceph_args(self, user, conf=None, pool=None):

    if (not self._validate_string_args(user)):
        raise exception.BackupInvalidCephArgs((_("invalid    user    '%s'") % user))
    args = ['--id', user]
    if conf:
        args.extend(['--conf', conf])
    if pool:
        args.extend(['--pool', pool])
    return args
