Created by: wojtuss

test=develop

This PR contains:

• fix for MKL-DNN pool2d op kernel reusing,
• unit test for QAT FP32 & INT8 inference output comparison.

The unit test is enabled for the following QAT pretrained models:

• ResNet50
• ResNet101
• GoogleNet
• MobileNetV1
• MobileNetV2
• VGG16
• VGG19 The unit test has FLAGS_use_mkldnn set to true.

The test is not enabled on CI as it fails on SKX machines due to s8s8s32 gemm issue in MKL-DNN: https://github.com/intel/mkl-dnn/issues/476. The issue is not present on CLX machines. It can be run manually, via e.g.

ctest -R test_qat_int8_resnet50_mkldnn

This test requires the TransformForMkldnnPass from the PR https://github.com/PaddlePaddle/Paddle/pull/17819.