Comment 1 for bug 1590647

Xenial Vagrant boxes are registered with Atlas to point at http://cloud-images.ubuntu.com/xenial/current/xenial-server-cloudimg-amd64-vagrant.box; a hiccup in our build system meant that that file did not successfully sync out from our build hosts.

I've kicked off another build, so this should be fixed by that, and we will be addressing that hiccup in the near future, so we shouldn't see repeats of this.