Fix ElementwiseOpInferVarType in elementwise_op to use the default InferVarType to find var recursively

Remove ElementwiseOpInferVarType in elementwise_op to use the default InferVarType to find var recursively

* Added kernel to is_empty_op

* Added python API

* Updated code as required

* Updated unittests

* "a piece of job."

* "fix typeo"

* "fix ci"

* listen_and_serv use localscope

* fix ut

- Finished draft of pooling reusing of operators

- Using gethash in PoolGrad added

- Removed diagnostic

- Added pool mkldnn grad reusing of primitives

- Added diagnostic

- Removed diagnostic

- added dependency to mkldnn data type for pooling mkldnn

- Added mkldnn memory data type determining based on template type of op

- Compilation warning fix

- codying style fixes

* fix cmake error

* update fix

In multi-thread condition, EnableProfiler can
be called after RecordEvent is constructed. In this
case, RecordEvent constructor will not init anything,
but RecordEvent destructor will do something since EnableProfiler
was called.
This PR fixes it.

* Fix a bug related to dispensable inputs and refine the inference unittest.

* Fix the use of dispensable inputs in reshape_op.

* Polish the enforce statements.

* Fix an English writing typo.