[Feat] Add CheckpointManager support with TFRA Dynamic Embedding Horovod Training.

[MoFHeka]

Description

Now CheckpointManager is available in Deepray when training with TFRA Dynamic Embedding.

[fix] In deepray/core/base_trainer.py, gpu_affinity didn't take effect when NVML Shared Library Not Found.
[fix] In deepray/core/base_trainer.py line 784, self.loss_container.metrics may empty when 'FLAGS.stop_steps = 0' in tools/testing/horovod_sync_train_test.py.

Also the adding script also support test TF Embedding when use Horovod training.

Type of change

• Bug fix
• New Tutorial
• Updated or additional documentation
• Additional Testing
• New Activation and the changes conform to the activation contribution guidelines
• New Callback and the changes conform to the callback contribution guidelines
• New Image addition and the changes conform to the image op contribution guidelines
• New Layer and the changes conform to the layer contribution guidelines
• New Loss and the changes conform to the loss contribution guidelines
• New Metric and the changes conform to the metric contribution guidelines
• New Optimizer and the changes conform to the optimizer contribution guidelines
• New RNN Cell and the changes conform to the rnn contribution guidelines
• New Seq2seq addition and the changes conform to the seq2seq contribution guidelines
• New Text addition and the changes conform to the text op contribution guidelines

Checklist:

• I've properly formatted my code according to the guidelines
  • By running find ./ -name '*.py' -exec yapf --style=./.yapf -ir {} ;
  • By running pre-commit hooks
• This PR addresses an already submitted issue for Deepray
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• This PR contains modifications to C++ custom-ops

How Has This Been Tested?

mpirun -np 2 -H localhost:2 --allow-run-as-root pytest -v tools/testing/horovod_sync_train_test.py

or

horovodrun -np 2  pytest -v tools/testing/horovod_sync_train_test.py

[fuhailin]

With the latest TFRA, please rename DEHvdCheckpoint to DECheckpoint

[MoFHeka]

Rebase to #57