Split kubelet server initialization into two parts

First is initializing a KubeletConfig that starts no background
processes. Second is running the config. Provide a legacy path
that won't impact older callers while making it easier to customize
the interfaces passed to the Kubelet.

Used by OpenShift to inject some custom interfaces to the Kubelet
for config management.

cmd/kubelet/kubelet.go

@@ -43,7 +43,7 @@ func main() {
 
 	verflag.PrintAndExitIfRequested()
 
-	if err := s.Run(pflag.CommandLine.Args()); err != nil {
+	if err := s.Run(nil); err != nil {
 		fmt.Fprintf(os.Stderr, "%v\n", err)
 		os.Exit(1)
 	}