Validate the trained model against holdout games.

  Args:
    state: the RL loop State instance.
    holdout_glob: a glob that matches holdout games.

async def validate(state, holdout_glob):
  """Validate the trained model against holdout games.

  Args:
    state: the RL loop State instance.
    holdout_glob: a glob that matches holdout games.
  """

  if not glob.glob(holdout_glob):
    print('Glob "{}" didn\'t match any files, skipping validation'.format(
          holdout_glob))
  else:
    await run(
        'python3', 'validate.py', holdout_glob,
        '--flagfile={}'.format(os.path.join(FLAGS.flags_dir, 'validate.flags')),
        '--work_dir={}'.format(fsdb.working_dir()))