This is similar to image-build in terms of what it does, and somewhat
similar to OSBS phase in how it's implemented.
The phase reads configuration, submits the build via XMLRPC call and
waits for the task to finish. Then it downloads the built image and
includes it in the compose metadata.
JIRA: RHELCMP-315
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>
