Automatic merge from submit-queue (batch tested with PRs 62850, 63504). 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>.
Improve where we load builds from for kubeadm upgrade jobs
**What this PR does / why we need it**:
For 1.8,1.9,1.10 branches, we need to load the latest
version from ci/latest*.txt.
For master, we need to load the version number from
ci-cross/latest.txt
try these to verify:
```
gsutil cat gs://kubernetes-release-dev/ci/latest-1.9.txt
gsutil cat gs://kubernetes-release-dev/ci-cross/latest.txt
```
**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/kubernetes/issues/61483
**Special notes for your reviewer**:
**Release note**:
```release-note
Fixed where we get latest builds for stable branches
```
c94efcea1d