docs: def ostree_compose(self, release):
          """Compose the OSTree in the mock container"""
          start = datetime.utcnow()
          treefile = os.path.join(release['git_dir'], 'treefile.json')
          cmd = release['ostree_compose'] % treefile
          with file(treefile, 'w') as tree:
              json.dump(release['treefile'], tree)
          # Only use new_chroot for the invocation, as --clean and --new-chroot are buggy together right now
          out, err, rcode = self.mock_chroot(release, cmd, new_chroot=True)
          ref = None
          commitid = None
          for line in out.split('\n'):
              if ' => ' in line:
                  # This line is the: ref => commitid line
                  line = line.replace('\n', '')
                  ref, _, commitid = line.partition(' => ')
          self.log.info('rpm-ostree compose complete (%s), ref %s, commitid %s',
                        datetime.utcnow() - start, ref, commitid)
          return ref, commitid