add vagrant style build for go_segment

This PR is to build a base box for go_segment to speed up our Jenkins build times. We were not able to get the packer approach to building boxes working, because of the private SG cookbooks. Instead we used Vagrant, Berkshelf, and `vagrant package` to build the box, see the README in `go_segment_base` directory.

Let me know if there are questions or feeback, or if you prefer I PR this to a topic branch since it's so different.
I think we'd rather omit Gemfile and Gemfile.lock and let workstation_setup be responsible for getting the tools on the box in general; otherwise, we now have two places to manage the Berkshelf and Chef versions.  The exception would be if we wanted to use a specifically different version of those tools here, but I think in this case, and for the foreseeable ones, we want it to match workstation_setup.