Allow a flag that forces kubelet to have a valid kubeconfig

--require-kubeconfig forces the kubelet to use the kubeconfig for all
APIserver communication, and exit cleanly.

cmd/kubelet/kubelet.go

@@ -44,7 +44,7 @@ func main() {
 	verflag.PrintAndExitIfRequested()
 
 	if err := app.Run(s, nil); err != nil {
-		fmt.Fprintf(os.Stderr, "%v\n", err)
+		fmt.Fprintf(os.Stderr, "error: %v\n", err)
 		os.Exit(1)
 	}
 }