Update zone status for all expired zones.

def _clear_expired_zones(self):
        """
        Update zone status for all expired zones.
        """
        zones = []

        for z in list(self._zones.keys()):
            zones += [z]

        for z in zones:
            if self._zones[z].status != Zone.CLEAR and self._zone_expired(z):
                self._update_zone(z, Zone.CLEAR)