Automatic merge from submit-queue (batch tested with PRs 55764, 55683, 55468, 54409, 55546). 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 join: Error out if CA pinning isn't used or opted out of
Signed-off-by: yuexiao-wang <wang.yuexiao@zte.com.cn>
**What this PR does / why we need it**:
convert the warning to an error in kubeadm
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes https://github.com/kubernetes/kubeadm/issues/534
**Special notes for your reviewer**:
/cc @mattmoyer
**Release note**:
```release-note
[action required] kubeadm join: Error out if CA pinning isn't used or opted out of
* kubeadm now requires the user to specify either the `--discovery-token-ca-cert-hash` flag or the `--discovery-token-unsafe-skip-ca-verification` flag.
```
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