Switch over to max_pool_v2 in Python (#14983)

* Switch over to max_pool_v2 in Python

This fix is a follow up to 11875 so that MaxPool in Python
use v2 version. As 11875 has been merged some time ago,
this fix conforms to the deprecation policy.

This fix is realted to 11875 and 4746.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Update test cases in contrib/specs/python/specs_test due to MaxPool -> MaxPoolV2

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Update tensorflow/contrib/receptive_field

Update tensorflow/contrib/receptive_field
due to max_pool's strides and ksize from  attr -> input

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Remove const restriction for strides and ksize

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Register MaxPoolV2 with XLA

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Reformat with clang-format -i --style=Google

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>