Report message.

def report_message(report):
    """Report message."""
    body = 'Error: return code != 0\n\n'
    body += 'Archive: {}\n\n'.format(report['archive'])
    body += 'Docker image: {}\n\n'.format(report['image'])
    body += 'Docker container: {}\n\n'.format(report['container_id'])
    return body