`kubeadm upgrade plan` takes an optional positional argument for the
target Kubernetes version [1], which is documented as
> To skip the internet check, pass in the optional [version] parameter
In light of RFC 015, we should not do an "internet check" for latest
versions, but stick to the version we're actually targeting with the
upgrade. Thus, we explicitly pass the version as an argument.
[1]: https://kubernetes.io/docs/reference/setup-tools/kubeadm/kubeadm-upgrade/#cmd-upgrade-plan
There used to be three definitions of a Component type, and conversion
routines between the three. Since the use case is always the same, and
the Component semantics are defined by versions.go and the installer, it
seems appropriate to define the Component type there and import it in
the necessary places.
