orca tf estimator change to tf.train.optimizer (#2380)
orca tf estimator change to tf.train.optimizer (#2380)

* change to tf.train.optimizer

* fix style
intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,intel-analytics/BigDL