Create the config file from the defaults under the given name.

def create_config(config_fname, override_url=None):
    '''
    Create the config file from the defaults under the given name.
    '''
    config_path = os.path.dirname(config_fname)
    os.makedirs(config_path, exist_ok=True)

    # Consider override URL. Only used by test suite runs
    settings = DEFAULT_SETTINGS_FLAT
    if override_url:
        settings['url'] = override_url

    # Create fresh config file, including new UUID
    with open(config_fname, 'wt') as config:
        config.write(DEFAULT_FILE_CONTENT.format(**settings))
    return True