Issue 4: Fixed bug where VariableInfo equality fails when _FillValue is np.nan

[stephenykp]

Github Issue: #4

Description

The granule variable equality check is failing for the granules tested in #4. This leads to

2021-11-17T16:52:52.435Z [debug]: FROM WORKER LOG: ERROR:root:Variable schemas are inconsistent between granules

Overview of work done

Because of the following:

>>> np.nan == np.nan
False

we are seeing errors if the _FillValue is np.nan, because the equality check fails. Added an extra check if the equality check fails

>>> np.array_equal(np.nan, np.nan, equal_nan=True)
True

Overview of verification done

• Added a unit test for _FillValue = np.nan case
• Tested on Concise input granules attached to Error when trying to run l2ss-concise chain in Harmony #4.

Overview of integration done

N/A

PR checklist:

• Linted
• Updated unit tests
• Updated changelog
• Integration testing

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