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>.
kubeadm: add better test coverage to reset.go
**What this PR does / why we need it**:
a PR for adding some more tests in `kubeadm/cmd` for `reset.go`.
increasing coverage from ~11% to ~92%
the remaining 8% are kind of hard to test or not worth the complexity.
original idea to add more tests in kubeadm was suggested to me by @luxas at slack.
in time, i might add better coverage to all cmd `.go` files.
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
please, link issue # if you know of such.
**Special notes for your reviewer**:
none
**Release note**:
```release-note
NONE
```
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