remove hard configuration of coreos.dev as the hostname for the default site

Tried this out with `vagrant ssh` and then
````bash
sudo sh /data/infrastructure/scripts/setup.sh
sudo systemctl reload haproxy
````
and it worked. It didn't work with just `vagrant up` or `vagrant provision` on the branch, though. But maybe that was because the VM was already running.

The 'coreos.dev' hostname is still being set in the Vagrantfile now, but no longer hard-coded in anything that's called by the setup.sh script (renamed from vagrant.sh)