KubernetesVersion sent by the init command now controls
all downloaded binaries, if they depend on the k8s version.
* Move all download links into /internal/versions.
* Unify files in /internal/versions package
* Move image download links into VersionConfigs
and thus make them dependant on the k8s version,
where the image version is specific to the k8s version.
* Don't specify patch version in k8sVersion
AB#2074: Add configurable k8s version
Configurable version flow:
* cli config holds/validates k8sVersion
* InitCluster receive a k8sVersion arg
* InitCluster creates CM "k8s-version"
* kubeadm's InitConfiguration receives k8sVersion
* joinservice spec mounts/reads k8s-version CM
* joinservice supplies k8sVersion via JoinTicketResponse
Other changes:
* Remove unused test code (FakeK8SClient)
* move VersionConfig map to /internal/versions
* installk8sComponents is now a function instead of a method
