change box_url to be the same as controller

right now, we have our default Vagrantfile pointing its box_url to https://oss-binaries.phusionpassenger.com/vagrant/boxes/ubuntu-12.04.3-amd64-vbox.box. All Deis nodes should be on the same base VM so that we are consistent.

Also note that the reason why I hit https://github.com/opdemand/deis/pull/528#issuecomment-36702990 was because of this. I did not have a `deis-node` box under `~/.vagrant.d/boxes`, so the timeout issue was from having to re-download the same box, just with a different name.