Automatic merge from submit-queue (batch tested with PRs 47416, 47408, 49697, 49860, 50162)
kubeadm: Replace *clientset.Clientset with clientset.Interface
**What this PR does / why we need it**:
Needed for https://github.com/kubernetes/kubernetes/pull/48899
We should always use `clientset.Interface` instead of `*clientset.Clientset`, for better testability and all the other benefits of using an interface.
**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**:
Should be straightforward to merge
**Release note**:
```release-note
NONE
```
@timothysc @dmmcquay @pipejakob
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