Collect metrics from all registered metric sets
        :return:

def collect(self):
        """
        Collect metrics from all registered metric sets
        :return:
        """
        logger.debug("Collecting metrics")

        for name, metricset in compat.iteritems(self._metricsets):
            data = metricset.collect()
            if data:
                self._queue_func(constants.METRICSET, data)