call cmds to start tensorboard process in local machine

def start_tensorboard_process(args, nni_config, path_list, temp_nni_path):
    '''call cmds to start tensorboard process in local machine'''
    if detect_port(args.port):
        print_error('Port %s is used by another process, please reset port!' % str(args.port))
        exit(1)
    
    stdout_file = open(os.path.join(temp_nni_path, 'tensorboard_stdout'), 'a+')
    stderr_file = open(os.path.join(temp_nni_path, 'tensorboard_stderr'), 'a+')
    cmds = ['tensorboard', '--logdir', format_tensorboard_log_path(path_list), '--port', str(args.port)]
    tensorboard_process = Popen(cmds, stdout=stdout_file, stderr=stderr_file)
    url_list = get_local_urls(args.port)
    print_normal(COLOR_GREEN_FORMAT % 'Start tensorboard success!\n' + 'Tensorboard urls: ' + '     '.join(url_list))
    tensorboard_process_pid_list = nni_config.get_config('tensorboardPidList')
    if tensorboard_process_pid_list is None:
        tensorboard_process_pid_list = [tensorboard_process.pid]
    else:
        tensorboard_process_pid_list.append(tensorboard_process.pid)
    nni_config.set_config('tensorboardPidList', tensorboard_process_pid_list)