Example usage::

        >>> from ceph_deploy.util.paths import mon
        >>> mon.keyring('mycluster', 'myhostname')
        /var/lib/ceph/tmp/mycluster-myhostname.mon.keyring

def keyring(cluster, hostname):
    """
    Example usage::

        >>> from ceph_deploy.util.paths import mon
        >>> mon.keyring('mycluster', 'myhostname')
        /var/lib/ceph/tmp/mycluster-myhostname.mon.keyring
    """
    keyring_file = '%s-%s.mon.keyring' % (cluster, hostname)
    return join(constants.tmp_path, keyring_file)