PEP 8 and more idiomatic code in image/tests/test_resample.py

Use spaces instead of tabs and also use ``is None`` or ``is not None``
instead of ``== None`` or ``!= None``, respectively.
Merge pull request #966 from derdon/test_resample

[BugFix]: PEP 8 and more idiomatic code in image/tests/test_resample.py