Saves current model to checkpoint folder.
        :param steps: Current number of steps in training process.
        :param saver: Tensorflow saver for session.

def _save_model(self, steps=0):
        """
        Saves current model to checkpoint folder.
        :param steps: Current number of steps in training process.
        :param saver: Tensorflow saver for session.
        """
        for brain_name in self.trainers.keys():
            self.trainers[brain_name].save_model()
        self.logger.info('Saved Model')