message: Update all the TPUStrategy examples to use the new v2 APIs, i.e.
  make_dataset_iterator -> experimental_distribute_dataset,
  make_input_fn_iterator -> experimental_distribute_datasets_from_function,
  unwrap -> experimental_local_results,
  experimental_run -> experimental_run_v2
diff: @@ -129,13 +129,15 @@ def main(argv):
  with tf.control_dependencies([update_loss, update_accuracy]):
  return tf.identity(loss)
  - train_iterator = strategy.make_dataset_iterator(train_ds)
  - test_iterator = strategy.make_dataset_iterator(test_ds)
  -
  - dist_train = strategy.unwrap(
  - strategy.experimental_run(train_step, train_iterator))
  - dist_test = strategy.unwrap(
  - strategy.experimental_run(test_step, test_iterator))
  + train_iterator = strategy.experimental_distribute_dataset(
  + train_ds).make_initializable_iterator()
  + test_iterator = strategy.experimental_distribute_dataset(
  + test_ds).make_initializable_iterator()
  +
  + dist_train = strategy.experimental_local_results(
  + strategy.experimental_run_v2(train_step, args=(next(train_iterator),)))
  + dist_test = strategy.experimental_local_results(
  + strategy.experimental_run_v2(test_step, args=(next(test_iterator),)))
  training_loss_result = training_loss.result()
  training_accuracy_result = training_accuracy.result()
  