* Add calibration README; test=develop

* Add INT8 calibration support in Paddle package; test=develop

* Enable pool2d operator for a ngraph engine
test=develop

* Update
test=develop

* move var strusted to vars_distributed.py, add optimizer's block name, test=develop

* rename optimzier's seems complex, revert it, test=develop

* replace * with details, test=develop

* Enable performance measurement in INT8 calibration unit test

test=develop

* Some improvements to support bert mixed precision training

test=develop

* Revert the cast in layer_norm

test=develop

* Refine beam_search_op to output an extra parent_idx tensor.
test=develop

* Fix the unittest test_beam_search_op.
test=develop

* Fix the merging mistake.
test=develop

test=develop

test=develop

* fix default create_parameter dtype maching initializers test=develop

* update type check test=develop

* update test=develop

test=develop

test=develop

test=develop

test=develop