Add support for Vagrant-based VM testing on Windows and Linux using the gpii-ci plugin

[colinbdclark]

The vagrant-gpii-ci plugin can orchestrate the process of running an automated test suite across multiple VMs. It would be great to be able to run all of osc.js' test suite on Linux and Windows (in addition to my on Mac-based host, which is of course more complex to virtualize due to licensing issues of macOS).

We should add support for it to osc.js. Flocking's implementation will provide a good starting point for doing so.