test=develop

* Enable cross_entropy operator for a ngraph engine
test=develop

* Update tests
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* Added PADDLE_ENFORCE for the batch_norm operator
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* Update the message about which format are supported right now
test=develop

* Correct the comment in control_flow.py.

* Correct the argument list of ops.
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* Update API.spec.
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* Skip op_callstack attr for all op apis.
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* Remove use_mkldnn and is_test from python api.
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* Remove use_mkldnn and is_test from op_proto_maker and hard-coding them in python when generating doc string.
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1.Remove the code for setting mkldnn environment in the test_calibration.py;
2.Update the cmake file for MKLDNN environment enabling;
3.Update the INT8 inference doc.

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* fix group_norm

* test=develop

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* remove est_image_classification_resnet for mac
test=develop

* increate the timeout
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* Added ngraph sum op test=develop

* Added sigmoid, relu_grad and tanh_grad test=develop

* remove duplicates test=develop

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* add launch mp distributed mode module test=develop

* delete unused file test=develop

* refine usage test=develop

* refine usage test=develop

* move distributed package test=develop

* add to whl package test=develop

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* 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

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