Update C API test data comparison for s390x (#15390)

* Correct the AppendHash test data comparison for s390x

* Correct _USE_C_API test data comparison for s390x

* Correcting the Python coding style (pylint)

Correcting the following comment issued by pylint:
C: 25, 0: standard import "import platform" should be placed before "import numpy as np" (wrong-import-order)

* Correcting code to conform to Google C++ Style Guide

Correcting as per the changes suggested by "clang-format".

* Making the changes generic for all big endian architectures

Changes made as per review comment: https://github.com/tensorflow/tensorflow/pull/15390#pullrequestreview-84306138

* Making the changes generic for all big endian architectures

Changes made as per review comment: https://github.com/tensorflow/tensorflow/pull/15390#discussion_r157631673

* Correcting code to conform to Google C++ Style Guide