Automatic merge from submit-queue (batch tested with PRs 59965, 59115, 63076, 63059). 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>.
Prepull etcd before an upgrade
If kubeadm ever has to upgrade etcd it should prepull the image so
there is less downtime during the upgrade when etcd versions change.
Fixeskubernetes/kubeadm#669
Signed-off-by: Chuck Ha <ha.chuck@gmail.com>
**What this PR does / why we need it**:
This PR Prepulls the etcd image during a `kubeadm upgrade apply`.
**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#669
**Special notes for your reviewer**:
constants.MasterComponents was not changed because it is used in many places where etcd does not need to be nor should it be a part of this slice.
**Release note**:
```release-note
NONE
```
/cc @kubernetes/sig-cluster-lifecycle-pr-reviews
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