* Remove the NGraph engine from PDPD repository
1. Each operator was removed from the operator's directory
2. Each test was removed from the unittest directory
3. The parallel executor support was removed from the PDPD
4. The CMake file was removed from the PDPD
5. The NG flags were removed from the repository
test=develop

* Remove ngraph from:
1. Cmake file
2. Python file
test=develop

add cp27-cp27m-gcc82 and cp27-cp27mu-gcc82 branch to support gcc8.2 compile for paddle, test=develop (#22504)

* polish grad op check, test=develop, test=document_fix

* keep op_use_default_grad_maker.spec to avoid conflict, test=develop, test=document_fix

Add coverage data processing tools.

* add shell scripts. test=develop

* rename test_pybind_inference to test_pybind_interface and print repeat process in check_op_desc.py. test=develop

* add approval RD. test=develop

* add data_type register CI test=develop

* add op add test case test=develop

* add test case for register op kernel test=develop

* fix shell script bug test=develop

* fix checkout branch test=develop

* remove test case code test=develop

* fix op_type.spec name test=develop

* fix default grad op maker ci bug, test=develop, test=document_fix

* remove some ops from paddle/fluid/op_use_default_grad_op_maker.spec, test=develop, test=document_fix

* add unused input vars check for OpWithKernel, test=develop

* remove unused vars in some ops, test=develop

* fix batch_norm, test=develop

* add white list, test=develop

* add CI check for white list, test=develop

* :ove white list to c++, test=develop

* solve failure of CI, test=develop

* add unittest for unused_var_check, test=develop

* refine code, enable check in operator_test, test=develop

* skip mkldnn, test=develop

* extend white list, test=develop

* refine condition of mkldnn, test=develop

* fix paddle_build, test=develop

* follow comments, test=develop

* fix GetExpectedKernelType

* add wiki ref to err_msg, test=develop

* follow comment, test=develop

* add ending message

Add ending message to indicate script execution properly finished

* Update paddle_build.sh

test=develop

* Update paddle_build.sh

test=document_fix

* Update paddle_build.sh

test=develop test=document_fix

* split api_spec document;test=document_fix

* change tools

* test=develop;test=document_fix

* test=develop;test=document_fix

* test=develop

* mv sampcd_processor.py to tools

test=develop test=document_fix

* update example script

test=develop test=document_fix

test=develop

* refine API.spec, test=develop

* add nn.py to test,test=develop

* fix by removing new.spec, test=develop, test=document_fix

* refine scripts when PYTHON_ABI is empty, follow partial comments, add extra cpp api doc, test=develop, test=document_fix

* remove extra doc changes, remove API.spec, test=develop

This PR fix the tag error in paddle_build.sh

* refine print_signatures.py to remove ComposeNotAligned, test=develop

* remove experimental_namespace, test=develop

* add train demo to paddle_build.sh

test=develop
test=document_preview

* code cleaning

* test=develop

test=develop

* remove program desc files

test=develop

* add test_train to CI

test=develop
test=document_preview

* make run.sh excutable

test=develop
test=document_preview

* switch with_mkl to off

test=develop
test=document_preview

* switch with_mkl to off

test=develop

* switch with_mkl to on

test=develop

* move test_fluid_lib_train to ci_py35

test=develop

* fix bugs of MKLDNN building

* rm build_train_lib(), test=develop

* restore tensor.h, test=develop

* change approve site ;test=develop

* test=develop

* modify paddle_build.sh for Paddle python3 version image generation, test=develop

* modify paddle_build.sh for Paddle python3 image generation, test=develop

* add exception exit on error example codes test=develop