Created by: kinghuin

1. merge release/v1.4 to develop
2. solve logging problem thoroughly the code below can be deleted:

        for handler in logging.root.handlers[:]:
            logging.root.removeHandler(handler)

3. implement hook mechanism

Well test in:

    def func(self, run_states):
        logger.info("I am the new hook function")
        scores, avg_loss, run_speed = self._calculate_metrics(run_states)
        self.tb_writer.add_scalar(
            tag="Loss_{}".format(self.phase),
            scalar_value=avg_loss,
            global_step=self._envs['train'].current_step)
        log_scores = ""
        for metric in scores:
            self.tb_writer.add_scalar(
                tag="{}_{}".format(metric, self.phase),
                scalar_value=scores[metric],
                global_step=self._envs['train'].current_step)
            log_scores += "%s=%.5f " % (metric, scores[metric])
        logger.info("step %d / %d: loss=%.5f %s[step/sec: %.2f]" %
                    (self.current_step, self.max_train_steps, avg_loss,
                     log_scores, run_speed))

    def func1(self, run_states):
        logger.info("modify fuction can get self.best_score=%s and len(run_states)=%s"
                    % (self.best_score, len(run_states)))

    def func2(self, run_states):
        logger.info("second hook can get self.best_score=%s and len(run_states)=%s" %
                    (self.best_score, len(run_states)))

    cls_task.delete_hook("log_interval", "default")
    print(cls_task.hooks)
    cls_task.add_hook("log_interval", "add", func)
    cls_task.add_hook("log_interval", "modified", func)
    print(cls_task.hooks)
    cls_task.modify_hook("log_interval", "modified", func1)
    cls_task.add_hook("log_interval", func2)
    try:
        cls_task.add_hook("log_interval", 000, func)
    except Exception as e:
        print(e)
    try:
        cls_task.add_hook("log_interval", 111)
    except Exception as e:
        print(e)
    try:
        cls_task.add_hook("log_interval")
    except Exception as e:
        print(e)
    try:
        cls_task.add_hook("xxx_interval", func)
    except Exception as e:
        print(e)
    try:
        cls_task.delete_hook("xxx_interval", "xxx")
    except Exception as e:
        print(e)
    try:
        cls_task.delete_hook("log_interval", "xxx")
    except Exception as e:
        print(e)
    try:
        cls_task.modify_hook("log_interval", "xxx", func)
    except Exception as e:
        print(e)
    try:
        cls_task.modify_hook("log_interval", "modified", 111)
    except Exception as e:
        print(e)