get the file name of config file

def get_config_filename(args):
    '''get the file name of config file'''
    experiment_id = check_experiment_id(args)
    if experiment_id is None:
        print_error('Please set the experiment id!')
        exit(1)
    experiment_config = Experiments()
    experiment_dict = experiment_config.get_all_experiments()
    return experiment_dict[experiment_id]['fileName']