Merge pull request #56599 from xiangpengzhao/kubeadm_stable_v19_version

Automatic merge from submit-queue (batch tested with PRs 56599, 56824, 56918, 56967, 56959). 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: Use the v1.9 branch by default

**What this PR does / why we need it**:
As per https://github.com/kubernetes/kubeadm/blob/master/docs/release-cycle.md, bump the default Kubernetes version to use in kubeadm right before v1.9.0-rc.1 (or maybe rc.0 ?) is cut.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
ref: #47440 #52085

**Special notes for your reviewer**:
/cc @luxas @kubernetes/sig-cluster-lifecycle-pr-reviews @kubernetes/kubernetes-release-managers

**Release note**:

```release-note
NONE
```

Author: Kubernetes Submit Queue

cmd/kubeadm/app/apis/kubeadm/v1alpha1/defaults.go

@@ -39,7 +39,7 @@ const (
 	// DefaultClusterDNSIP defines default DNS IP
 	DefaultClusterDNSIP = "10.96.0.10"
 	// DefaultKubernetesVersion defines default kubernetes version
-	DefaultKubernetesVersion = "stable-1.8"
+	DefaultKubernetesVersion = "stable-1.9"
 	// DefaultAPIBindPort defines default API port
 	DefaultAPIBindPort = 6443
 	// DefaultAuthorizationModes defines default authorization modes