[WIP] new crowbar_autobuild batch script

**This is work in progress; do not merge yet.**  It's provided so that people can try it out if they want.

    crowbar autobuild foo.yaml

will automatically create (if necessary), edit, and apply all proposals described within `foo.yaml`.  This enables building arbitrary cloud configurations in an entirely automated fashion, which can be very useful for testing, building reproducible demos, and eventually maybe even partially mimicking customer environments.