Automatic merge from submit-queue. 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>.
Regenerate API server serving certificates when upgrading.
**What this PR does / why we need it**:
TODO:
- [x] check the age of crt.
- [x] check the new version number.
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes https://github.com/kubernetes/kubeadm/issues/548
**Special notes for your reviewer**:
/cc @luxas
**Release note**:
```release-note
NONE
```
991e33d36a