Automatic merge from submit-queue (batch tested with PRs 41701, 41818, 41897, 41119, 41562)
kubeadm: Secure the control plane communication and add the kubeconfig phase command
**What this PR does / why we need it**:
This generates kubeconfig files for the controller-manager and the scheduler, ref: https://github.com/kubernetes/kubeadm/issues/172
The second commit adds the `kubeadm alpha phase kubeconfig` command as described in the design doc: https://github.com/kubernetes/kubeadm/pull/156
**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**:
@dmmcquay What kind of tests would you like for the kubeconfig phase command?
**Release note**:
```release-note
```
@jbeda @mikedanese @dmmcquay @pires @liggitt @deads2k @errordeveloper
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