Automatic merge from submit-queue (batch tested with PRs 49849, 50334, 51414)
kubeadm: Use the --enable-bootstrap-token-auth flag when possible
**What this PR does / why we need it**:
Uses the right API server flag for the right version.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #
fixes: https://github.com/kubernetes/kubeadm/issues/414
**Special notes for your reviewer**:
**Release note**:
```release-note
NONE
```
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