GitLab

**Description**
Fix bug of duration feature for model benchmarks in distributed mode.

**Major Revision**
- Add all_reduce to sync the result of is_finished(the function to judge whether the model benchmark should be stopped) in each step 
  - to avoid inconsistency between different ranks to determine duration end (some rank may enter one more step and can never finish)
- Add torch.cuda.synchronize() before and after step time measuring in train_step() for all model benchmarks
  - some operations in train_step() maybe async resulting incorrect step time records (for example, lstm) 

* Benchmarks: Add Benchmark - Add LSTM model benchmarks.

* Benchmarks: Add Benchmark - Add GPT2 model benchmark.

Benchmarks: Add Benchmark - Add Pytorch BERT benchmarks, including bert-base and bert-large.   (#20)

* add pytorch bert benchmarks.

* revise code

* fix issue

* revise code.
Co-authored-by: Guoshuai Zhao <guzhao@microsoft.com>