It will take RPM repo from a variant in this compose and a Dockerfile
from configured git and use it to build an image.
The build images are uploaded to some a Docker registry by OSBS and are
not directly part of compose (because there is no export function).
There is a new metadata file `osbs.json` that has some information that
can be used to find the image.
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>