Automatic merge from submit-queue (batch tested with PRs 56390, 56334, 55572, 55598, 56563). 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>.
add apiServerCertSANs case for test GetAltNames
**What this PR does / why we need it**:
When fix#55566 , found there is not test case for apiServerCertSANs
**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 #
**Special notes for your reviewer**:
assgin @luxas
**Release note**:
```release-note
NONE
```
We allow a kubeadm user to use an external CA by checking to see if ca.key is missing and skipping cert checks and kubeconfig generation if ca.key is missing.
Allow to specify a node-name instead of relaying in `os.Hostname()`
This is useful where kubelet use the name given by the cloud-provider to
register the node.
Partially fix: kubernetes/kubeadm#64
