* Refactor to create MKLDNN primitives on the first iteration:
  add, avg_pool, batch_norm, bounded_relu, concat, convert_layout,
  leaky_relu, lrn, max_pool, quantized_avg_pool, quantized_max_pool,
  relu, sigmoid, slice, softmax.

* Refactor to create MKLDNN primitives on the first iteration:
  pooling backward, convolution.

* Refactor to create MKLDNN primitives on the first iteration:
  convolution backward, rnn, lstm, quantization, dequantization.

* Delete one duplicate declaration.

* Create and pass mkldnn descriptors/primitive-descriptors for ops.

* Create and pass mkldnn descriptors for convolution backward ops.

* Remove one unused variable.

* Remove unused variables.

* Remove unused variables.

* Address PR feedback.

* Fix a bug.

* Add one parameter to build_quantize_reorder.

* Address PR feedback.

* Fix bi-rnn issue.