Updates a zones status.

        :param zone: zone number
        :type zone: int
        :param status: zone status
        :type status: int

        :raises: IndexError

def _update_zone(self, zone, status=None):
        """
        Updates a zones status.

        :param zone: zone number
        :type zone: int
        :param status: zone status
        :type status: int

        :raises: IndexError
        """
        if not zone in self._zones:
            raise IndexError('Zone does not exist and cannot be updated: %d', zone)

        old_status = self._zones[zone].status
        if status is None:
            status = old_status

        self._zones[zone].status = status
        self._zones[zone].timestamp = time.time()

        if status == Zone.CLEAR:
            if zone in self._zones_faulted:
                self._zones_faulted.remove(zone)

            self.on_restore(zone=zone)
        else:
            if old_status != status and status is not None:
                self.on_fault(zone=zone)