bob tf predict_bio has a bug in checkpoint loading step

tf.estimator.Estimator.predict and .evaluate take a checkpoint parameter. This value must be a tensorflow checkpoint prefix (e.g. /model_dir/model.ckpt-23952000) but I wanted to point to a folder instead and wanted to pickup the latest checkpoint from there automatically so this script can be used in parallel with bob tf eval. However, looks like there is a bug in https://gitlab.idiap.ch/bob/bob.learn.tensorflow/blob/9c068090975ab5cb13d738048017ff3b648c1bb7/bob/learn/tensorflow/script/predict_bio.py#L226 where estimator.model_dir is used as input to tf.train.get_checkpoint_state instead of checkpoint. This means the --checkpoint option had no effect so far :(