Following from #27830, this copies the source onto the instance and
displays the location of it prominently (keeping the download link for
anyone that just wants to curl it).

Example output (this tag doesn't exist yet):

---
Welcome to Kubernetes v1.4.0!

You can find documentation for Kubernetes at:
  http://docs.kubernetes.io/

The source for this release can be found at:
  /usr/local/share/doc/kubernetes/kubernetes-src.tar.gz
Or you can download it at:
  https://storage.googleapis.com/kubernetes-release/release/v1.4.0/kubernetes-src.tar.gz

It is based on the Kubernetes source at:
  https://github.com/kubernetes/kubernetes/tree/v1.4.0

For Kubernetes copyright and licensing information, see:
  /usr/local/share/doc/kubernetes/LICENSES
---