Return the calculator for the given `counter_type`.
        Fallback with `get_raw`.

def _get_property_calculator(self, counter_type):
        """
        Return the calculator for the given `counter_type`.
        Fallback with `get_raw`.
        """
        calculator = get_raw
        try:
            calculator = get_calculator(counter_type)
        except UndefinedCalculator:
            self.logger.warning(
                u"Undefined WMI calculator for counter_type {counter_type}."
                " Values are reported as RAW.".format(counter_type=counter_type)
            )

        return calculator