We should stop special casing "ci-cross" and just use the
configuration in test-infra to dictate where we pick up
the builds from.
For 1.8,1.9,1.10 branches, we need to load the latest
version from ci/latest*.txt.
For master, 1.11 etc, we need to load from ci-cross/latest*.txt.
We need to update test-infra configs if things fail.
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
```
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