def create_run_logfile(folder):
    """Create a 'run.log' within folder. This file contains the time of the
       latest successful run.
    """
    with open(os.path.join(folder, "run.log"), "w") as f:
        datestring = datetime.datetime.utcnow().strftime("%Y-%m-%d %H:%M:%S")
        f.write("timestamp: '%s'" % datestring)
Create a 'run.log' within folder. This file contains the time of the
       latest successful run.