Rework hostfs metrics

Ephemeral storage usage should be calculated by the metrics code,
not the eviction code.

pkg/kubelet/kubelet_test.go

@@ -250,13 +250,17 @@ func newTestKubeletWithImageList(
 	volumeStatsAggPeriod := time.Second * 10
 	kubelet.resourceAnalyzer = serverstats.NewResourceAnalyzer(kubelet, volumeStatsAggPeriod)
 
+	fakeHostStatsProvider := stats.NewFakeHostStatsProvider()
+
 	kubelet.StatsProvider = stats.NewCadvisorStatsProvider(
 		kubelet.cadvisor,
 		kubelet.resourceAnalyzer,
 		kubelet.podManager,
 		kubelet.runtimeCache,
 		fakeRuntime,
-		kubelet.statusManager)
+		kubelet.statusManager,
+		fakeHostStatsProvider,
+	)
 	fakeImageGCPolicy := images.ImageGCPolicy{
 		HighThresholdPercent: 90,
 		LowThresholdPercent:  80,