kubeadm upgrade apply now is able to utilize all possible combinations
of version argument, including labels (latest, stable-1.8, ci/latest-1.9)
as well as specific builds (v1.8.0-rc.1, ci/v1.9.0-alpha.1.123_01234567889)

As side effect, specifying exact build to deploy from CI area is now also
possible in kubeadm init command.

Fixes: kubernetes/kubeadm#451