Automatic merge from submit-queue (batch tested with PRs 49498, 49192)
kubeadm: Make sure --config can be mixed with --skip-* flags
**What this PR does / why we need it**:
fixes: https://github.com/kubernetes/kubeadm/issues/352
**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 a cherrypick candidate
**Release note**:
```release-note
kubeadm: Fixes a small bug where `--config` and `--skip-*` flags couldn't be passed at the same time in validation.
```
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