Automatic merge from submit-queue
kubeadm: Remove some old comments
**What this PR does / why we need it**:
Removes old and outdated comments.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #
**Special notes for your reviewer**:
**Release note**:
```release-note
NONE
```
@dmmcquay
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
Automatic merge from submit-queue (batch tested with PRs 41061, 40888, 40664, 41020, 41085)
kubeadm: added tests cert/pkiutil pkg
raised coverage from ~37% to ~77%
**What this PR does / why we need it**: added tests to cert/pkiutil pkg and raised coverage from ~37% to ~77%
Adding unit tests is a WIP from #34136
**Special notes for your reviewer**: /cc @luxas @pires
**Release note**:
```release-note
NONE
```
Automatic merge from submit-queue (batch tested with PRs 40187, 40231, 40152)
Update client/server cert generation utilities
Limit generated cert usage to client or server use.
Automatic merge from submit-queue (batch tested with PRs 37228, 40146, 40075, 38789, 40189)
Cleanup temp dirs
So funny story my /tmp ran out of space running the unit tests so I am cleaning up all the temp dirs we create.
