Create SessionRunHooks for all callbacks, and hook it onto `self.sess` to create `self.hooked_sess`.

        A new trainer may override this method to create multiple groups of hooks,
        which can be useful when the training is not done by a single `train_op`.

def initialize_hooks(self):
        """
        Create SessionRunHooks for all callbacks, and hook it onto `self.sess` to create `self.hooked_sess`.

        A new trainer may override this method to create multiple groups of hooks,
        which can be useful when the training is not done by a single `train_op`.
        """
        hooks = self._callbacks.get_hooks()
        self.hooked_sess = tfv1.train.MonitoredSession(
            session_creator=ReuseSessionCreator(self.sess), hooks=hooks)