This allows us to more concisely separate building from testing, which
in turn gives us a nicer inheritance pattern in our case.
See also: https://github.com/jlebon/redhat-ci/issues/11Closes: #569
Approved by: cgwalters
Add a YAML file for the new Red Hat CI framework.
Rather than re-installing all the build deps everytime, which takes
time, I added a Dockerfile that we can wire up to the Docker Hub. For
now it lives at `jlebon/ostree-tester:rhci`, but we can move it under
the `projectatomic` org (or a new `ostree` org).
Closes: #535
Approved by: cgwalters
Jonathan Lebon