* Enable momentum operator for a ngraph engine
test=develop

* Update tests
test=develop

* Unnecessary line of the code as intended was removed
test=develop

* Enable cross_entropy operator for a ngraph engine
test=develop

* Update tests
test=develop

* Added PADDLE_ENFORCE for the batch_norm operator
test=develop

* Update the message about which format are supported right now
test=develop

* Added ngraph sum op test=develop

* Added sigmoid, relu_grad and tanh_grad test=develop

* remove duplicates test=develop

test=develop

* fix compile issue with_distribute test=develop

* simplified logic test=develop

* use ngraph dependency test=develop

* set cpu only test=develop

* update test and eliminate fp16 test test=develop

* Added accuracy ngraph op test=develop

* fixed name type test=develop

test=develop

* Enable pool2d operator for a ngraph engine
test=develop

* Update
test=develop

* enable ngraph_engine_op
test=develop

* merge develop test=develop

* avoid const_cast test=develop

* rm ngraph_operator test=develop

* Added TODO to move EnableNgraph test=develop

* Add TODO to remove const_cast test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

* Enable mul operator for a ngraph
test=develop

* Enable activation ops test
test=develop

* Remove unused line
test=develop