Automatic merge from submit-queue (batch tested with PRs 51494, 56097, 56072, 56175). 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>.
Implement individual control for kubeadm preflight checks
**What this PR does / why we need it**:
With new flag `--ignore-checks-errors` user is able to
decrease severity of each individual check error to warning.
Old flag `--skip-preflight-checks` now acts as `--ignore-checks-errors=all` and will produce warnings.
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixeskubernetes/kubeadm#480
**Special notes for your reviewer**:
/area kubeadm
/sig cluster-lifecycle
cc @luxas
**Release note**:
```release-note
New kubeadm flag `--ignore-checks-errors` that enables to decrease severity of each individual error to warning.
Old flag `--skip-preflight-checks` is marked as deprecated and acts as `--ignore-checks-errors=all`
```
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