'Retrieves the list of supported metrics for this namespace and relay
name:
Name of the service bus namespace.
relay_name:
Name of the service bus relay in this namespace.
metric:
name of a supported metric
rollup:
name of a supported rollup
filter_expression:
filter, for instance "$filter=Timestamp gt datetime\'2014-10-01T00:00:00Z\'"'

def get_metrics_data_relay(self, name, relay_name, metric, rollup, filter_expresssion):

    response = self._perform_get(self._get_get_metrics_data_relay_path(name, relay_name, metric, rollup, filter_expresssion), None)
    return _MinidomXmlToObject.convert_response_to_feeds(response, partial(_ServiceBusManagementXmlSerializer.xml_to_metrics, object_type=MetricValues))
