Merge pull request #63812 from luxas/kubeadm_cut_kubelet_readonly_dep

Automatic merge from submit-queue (batch tested with PRs 57536, 63812). 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>.

kubeadm: Contact the kubelet on its healthz port instead of its readonly port

**What this PR does / why we need it**:
In order for us to disable the kubelet's readonly port in v1.11 (kubernetes/kubeadm#732), we need to cut the dependency on that port being open. Instead, we can use the dedicated healthz port (using the defaults `--healthz-bind-address=127.0.0.1` and `--healthz-port=10248`, xref: https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet/)

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Part of kubernetes/kubeadm#732

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```
@kubernetes/sig-cluster-lifecycle-pr-reviews @liztio

cmd/kubeadm/app/cmd/init.go

@@ -584,14 +584,7 @@ func waitForAPIAndKubelet(waiter apiclient.Waiter) error {
 
 	go func(errC chan error, waiter apiclient.Waiter) {
 		// This goroutine can only make kubeadm init fail. If this check succeeds, it won't do anything special
-		if err := waiter.WaitForHealthyKubelet(40*time.Second, "http://localhost:10255/healthz"); err != nil {
-			errC <- err
-		}
-	}(errorChan, waiter)
-
-	go func(errC chan error, waiter apiclient.Waiter) {
-		// This goroutine can only make kubeadm init fail. If this check succeeds, it won't do anything special
-		if err := waiter.WaitForHealthyKubelet(60*time.Second, "http://localhost:10255/healthz/syncloop"); err != nil {
+		if err := waiter.WaitForHealthyKubelet(40*time.Second, "http://localhost:10248/healthz"); err != nil {
 			errC <- err
 		}
 	}(errorChan, waiter)