Add Benchmark Script for Bert Models (#3829)
Add benchmark script for Transformer models
* Set intra_op_num_threads=1 for cpu (version <= 1.2.0)
* Add percentiles for latency
* torch.set_num_threads (for intra op) to get fair comparison
* Allow export ONNX model with specified number of inputs
* Add fusion statistics
* Install transformers from source
