Register a new metric set
        :param class_path: a string with the import path of the metricset class

def register(self, class_path):
        """
        Register a new metric set
        :param class_path: a string with the import path of the metricset class
        """
        if class_path in self._metricsets:
            return
        else:
            try:
                class_obj = import_string(class_path)
                self._metricsets[class_path] = class_obj(self)
            except ImportError as e:
                logger.warning("Could not register %s metricset: %s", class_path, compat.text_type(e))