Automatic merge from submit-queue (batch tested with PRs 51192, 55010). 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>.
Adding etcd upgrade option to kubeadm upgrade apply
This PR adds etcd upgrade functionality to kubeadm upgrade apply.
First commit adds certain functions to be able to deal with a single component of control plane and not just with all three components (apiserver, controller-manager and scheduler). It adds granularity as a result code can be reused.
Closes: https://github.com/kubernetes/kubeadm/issues/490
```release-note
Adds to **kubeadm upgrade apply**, a new **--etcd-upgrade** keyword. When this keyword is specified, etcd's static pod gets upgraded to the etcd version officially recommended for a target kubernetes release.
```
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