Fixed kube-up.sh to point to the right place.

With recent changes in apiserver, URL.Path == "/" simply returns http.StatusNotFound, instead of index.html anymore. But kube-up.sh still points to "/" at the end of building a new cluster. Fixed kube-up.sh to point to the right place.

This will have the result of causing ALL pages not handled otherwise to show our index page. I think it's necessary to add code in handleIndex that checks the path and only responds to "/" or reasonable variations of "/index.html".