build docker images to run mssh-copy-id (functional test)

def build_docker_run(ctx, image):
    """
    build docker images to run mssh-copy-id (functional test)
    """
    if image not in DOCKER_RUN_IMGS:
        print('Error: unknown docker image "{0}"!'.format(image), file=sys.stderr)
        sys.exit(1)

    # Build the RPM & deb
    if image in ('centos6', 'centos7'):
        build_rpm(ctx, target=image)
    elif image in ('ubuntu-trusty',):
        # TODO: add ubuntu-trusty
        build_deb(ctx, target=image)

    dinfo = DOCKER_RUN_IMGS[image]
    dinfo_work_dir = os.path.join(dinfo['path'], '_work')
    ctx.run('mkdir -p {0}'.format(dinfo_work_dir))
    ctx.run('cp {0} {1}'.format(os.path.join(DIST_DIR, 'mssh-copy-id-*.rpm'), dinfo_work_dir))
    ctx.run('docker rmi -f {0}'.format(dinfo['name']), warn=True)
    ctx.run('docker build -t {0} {1}'.format(dinfo['name'], dinfo['path']))