Without this patch SetKubernetesVersion does not set
a version in all locations where it's called, because
the passed config to it always has a default version
stable-1.
This always triggers the != "" check and the function
returns without setting a version.
Validate against DefaultKubernetesVersion and "" instead.
This fixes all cases where fetching a version from the internet
is not needed at all - e.g. "kubeadm token create".
Also make SetKubernetesVersion default to version.Get().String()
and add unit tests for the function.
fa9940c71c