Returns metric usage for client and its subhierarchy.

        Args:
            auth: <cik> for authentication
            resource: ResourceID
            metrics: Metric to measure (as string), it may be an entity or consumable.
            starttime: Start time of window to measure useage (format is ___).
            endtime: End time of window to measure useage (format is ___).

def usage(self, auth, resource, metric, starttime, endtime, defer=False):
        """ Returns metric usage for client and its subhierarchy.

        Args:
            auth: <cik> for authentication
            resource: ResourceID
            metrics: Metric to measure (as string), it may be an entity or consumable.
            starttime: Start time of window to measure useage (format is ___).
            endtime: End time of window to measure useage (format is ___).
        """
        return self._call('usage', auth,
                          [resource, metric, starttime, endtime], defer)