contains: catch wrong "multi elements contained expectation"

[Antonboom]

Bubbled while formatter.require-string-msg (#201) testing:

	assert.Contains(t, cadvisorInfoToUserDefinedMetrics(&cInfo),
		statsapi.UserDefinedMetric{
			UserDefinedMetricDescriptor: statsapi.UserDefinedMetricDescriptor{
				Name:  "qos",
				Type:  statsapi.MetricGauge,
				Units: "per second",
			},
			Time:  metav1.NewTime(timestamp2),
			Value: 100,
		},
		statsapi.UserDefinedMetric{
			UserDefinedMetricDescriptor: statsapi.UserDefinedMetricDescriptor{
				Name:  "cpuLoad",
				Type:  statsapi.MetricCumulative,
				Units: "count",
			},
			Time:  metav1.NewTime(timestamp2),
			Value: 2.1,
		})