Set CPU metrics for init containers under containerd

Copies PR kubernetes#76503 for release-1.11.

metrics-server doesn't return metrics for pods with init containers
under containerd because they have incomplete CPU metrics returned by
the kubelet /stats/summary API.

This problem has been fixed in 1.14 (kubernetes#74336), but the cherry-picks
dropped the usageNanoCores metric.

This change adds the missing usageNanoCores metric for init containers
in Kubernetes v1.11.

Fixes kubernetes#76292

pkg/kubelet/stats/cri_stats_provider.go

@@ -355,6 +355,7 @@ func (p *criStatsProvider) makeContainerStats(
 	} else {
 		result.CPU.Time = metav1.NewTime(time.Unix(0, time.Now().UnixNano()))
 		result.CPU.UsageCoreNanoSeconds = Uint64Ptr(0)
+		result.CPU.UsageNanoCores = Uint64Ptr(0)
 	}
 	if stats.Memory != nil {
 		result.Memory.Time = metav1.NewTime(time.Unix(0, stats.Memory.Timestamp))