Turns out I hit a nasty bug with vagrant 1.8.5 that can affect all kinds of *nix systems (but thankfully not Ubuntu 14.04 or Cumulus VX!).
I wrote a really quick script to make this easy for you to fix if you have hit this issue->
The problem presents itself as the vagrant image never boots. It will just hang on certain images. In my case CentOS7.2 from both boxcutter and CentOS/7 hashicorp images.