Added identity op and a fix for LRN (#9641)

* relu grad and maxpooling grad fixes for perf

* Graph layout pass and conversion pass changes

This commit makes following changes:

- Enables support for ReluGrad and BiasAddGrad
- Adds support for detecting depthwise/batchwise pooling
- Adds more unit tests for Graph rewrite pass
- Improvements to handling control-flow edges
- Bug fixes

* Defaulting to Eigen when LRN depth_radius!=2

* Fixed mkl_conv_grad_filter.cc for conv_ops_tests.py

* Style fix to mkl_matmul and remove unnecessary 'MKL' label on matmul kernel

* Style fixes based on clang-format to mkl_conv_* and mkl_matmul

* Bug fixes

* Adding OP_REQUIRES_OK check in Concat

* Making some style changes

* Enabled the configuration of MKL settings

* relu grad and maxpooling grad fixes for perf

* Graph layout pass and conversion pass changes

This commit makes following changes:

- Enables support for ReluGrad and BiasAddGrad
- Adds support for detecting depthwise/batchwise pooling
- Adds more unit tests for Graph rewrite pass
- Improvements to handling control-flow edges
- Bug fixes

* Defaulting to Eigen when LRN depth_radius!=2

* Fixed mkl_conv_grad_filter.cc for conv_ops_tests.py

* Style fix to mkl_matmul and remove unnecessary 'MKL' label on matmul kernel

* Style fixes based on clang-format to mkl_conv_* and mkl_matmul

* Bug fixes

* Adding OP_REQUIRES_OK check in Concat

* Making some style changes

* Enabled the configuration of MKL settings

* Fixing graph unit tests with Mkl op name change to _Mkl; Fixed missing _ in MklToTf op

* Fixed missing libdl.so.2 in BUILD file

* Fixes for unit test build failures.

* Changes in mkl_conv_grad_filter_ops.cc for Google code style

* Fixes to remove dead code

* removed the dead code and added a TODO for mkl implementation to handle this case in the future

* Enabling MklIdentityOp

* Calling MKL for all values of depth radius in LRN

* Fixed buildifier sanity check error

* Adding support for google's CI automation

* Updated link to new MKL version

* Enabling MklIdentityOp

* Calling MKL for all values of depth radius in LRN

* Fix for missing locate binary

* Fix for missing locate command in CI

* Adding updatedb to populate the database after installing mlocate

* Fixed buildifier issue

* setting tf_need_mkl=0 in libtf files

* Added third_party/mkl/* to .gitignore

* Added third_party/eigen3/mkl_include to .gitignore

* In configured, set MKL-enabling options only for Linux.

* Enabling MklIdentityOp

* Calling MKL for all values of depth radius in LRN

* Making style fix in LRN

* Fixed Indentation