Automatic merge from submit-queue (batch tested with PRs 60585, 62398, 62258, 62042). 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: surface external etcd preflight validation errors
**What this PR does / why we need it**:
This PR fixes a bug where errors that could occur while running preflight against an external etcd cluster were not being surfaced to the user.
**Which issue(s) this PR fixes** :
Fixes https://github.com/kubernetes/kubeadm/issues/719
**Release note**:
```release-note
kubeadm: surface external etcd preflight validation errors
```
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