Add kubernetes-test.tar.gz

Add test artifacts to the build. This lets you do:

tar -xzf kubernetes.tar.gz
tar -xzf kubernetes-test.tar.gz
cd kubernetes
go run ./hack/e2e.go -up -test -down

without having a git checkout.
Yeah - I didn't like it either, FWIW. I'll open an issue, because there's also some cleanup that could happen. (NOT IT. :))