Return the next batch of examples from validiation data set
        :param batch_size: int, size of image batch returned
        :return train_labels: list, of labels
        :return images: list, of images

def next_valid_batch(self, batch_size):
        """
        Return the next batch of examples from validiation data set
        :param batch_size: int, size of image batch returned
        :return train_labels: list, of labels
        :return images: list, of images
        """
        start = self.index_in_valid_epoch
        if self.index_in_valid_epoch + batch_size > self.num_valid_images:
            batch_size = 1
        self.index_in_valid_epoch += batch_size
        end = self.index_in_valid_epoch
        return self.valid_labels[start:end], self.img_norm(self.valid_images[start:end]), end, batch_size