[SPARK-26676][PYTHON] Make HiveContextSQLTests.test_unbounded_frames test compatible with Python 2 and PyPy
[SPARK-26676][PYTHON] Make HiveContextSQLTests.test_unbounded_frames test compatible with Python 2 and PyPy

## What changes were proposed in this pull request?

This particular test is being skipped at PyPy and Python 2.

```
Skipped tests in pyspark.sql.tests.test_context with pypy:
    test_unbounded_frames (pyspark.sql.tests.test_context.HiveContextSQLTests) ... skipped "Unittest < 3.3 doesn't support mocking"

Skipped tests in pyspark.sql.tests.test_context with python2.7:
    test_unbounded_frames (pyspark.sql.tests.test_context.HiveContextSQLTests) ... skipped "Unittest < 3.3 doesn't support mocking"
```

We don't have to use unittest 3.3 module to mock. And looks the test itself isn't compatible with Python 2.

This PR makes:
 - Manually monkey-patch `sys.maxsize` to get rid of unittest 3.3 condition
 - Use the built-in `reload` in Python 2, and `importlib.reload` in Python 3

## How was this patch tested?

Manually tested, and unit test is fixed.

Closes #23604 from HyukjinKwon/test-window.

Authored-by: Hyukjin Kwon <2680965ad5aae29275c8fb10150cb10f5554e78b@apache.org>
Signed-off-by: Bryan Cutler <060dd14c05a8ffa8f201883ef57d0676b7c9c04a@gmail.com>

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