Merge pull request #61053 from andrewsykim/kubelet-fix-flag-not-normalized

Automatic merge from submit-queue (batch tested with PRs 60772, 61011, 61053). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

kubelet initial flag parse should normalize flags instead of exiting

**What this PR does / why we need it**:
Sets normalize func for kubelet cleanFlagSet, otherwise kubelet will exit if non-normalized flag is used. For example, this happened on a kubelet running v1.10.0-beta.2:
```
F0312 17:59:03.138986   25317 server.go:144] unknown flag: --cluster_dns
```

This is where the kubelet exits: https://github.com/kubernetes/kubernetes/blob/master/cmd/kubelet/app/server.go#L142-L145. This would be a breaking change for anyone upgrading Kubernetes and using `_` in their flag names. 

```release-note
kubelet initial flag parse should normalize flags instead of exiting. 
```

cmd/kubelet/app/server.go

@@ -104,6 +104,7 @@ const (
 // NewKubeletCommand creates a *cobra.Command object with default parameters
 func NewKubeletCommand() *cobra.Command {
 	cleanFlagSet := pflag.NewFlagSet(componentKubelet, pflag.ContinueOnError)
+	cleanFlagSet.SetNormalizeFunc(flag.WordSepNormalizeFunc)
 	kubeletFlags := options.NewKubeletFlags()
 	kubeletConfig, err := options.NewKubeletConfiguration()
 	// programmer error