Automatic merge from submit-queue (batch tested with PRs 53204, 53364, 53559, 53589, 53088). 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>.
New version number for kubeadm constants.go
**What this PR does / why we need it**:
In kubeadm v1.9 the minimum kubelet & API Server version will be v1.8.0.
```release-note
NONE
```