Refactor folio-ansible for stable/testing

Work merged into master branch of folio-ansible

Added support for `dockerPull` Okapi launch descriptor parameter, so Okapi doesn't always upgrade the `testing` box on deployment.

This work is complete in branch of folio-ansible. , , and – I'm open to suggestions on how to roll it out with a minimum of disruption for developers and for the demo build.

One result of this work is that, instead of "folio-demo" and "folio-backend-auth" Vagrant boxes, there will be a "stable" and a "testing" Vagrant box, both containing the full FOLIO stack (with Stripes). I'm also open to suggestions on how to version these boxes – it's probably time to start with v1.0.0 for the "stable" box, not sure how to version the "testing" box.

I've built and uploaded both the "stable" and the "testing" boxes to Atlas (or will have done, by the time you read this), but I haven't made any announcements yet.

Simplified folio.yml to build full-stack for the "folio" group. "testing" group now deploys head-of-master for stripes components.

Next: how to build head-of-master platform for Stripes. Probably should simplify playbook to have just one set of roles for building a FOLIO system.