Training Startup

The key steps are as follows:

1. Define Saver to save and load a model during training. Start session calculation and call tf.compat.v1.train.Saver.save or tf.compat.v1.train.Saver.restore to respectively save or load a model during training.
2. Start a training job. For details, see Single-Server Single-Device and Single-Server Multi-Device Training.