BUG: Fix running DataProbe self test

This commit fixes the following error when running the DataProbe self
test from the SelfTests module:

Starting the test
Traceback (most recent call last):
  File "C:/dev/SN/Slicer-build/lib/Slicer-4.4/qt-scripted-modules/SelfTests.py", line 168, in run
result = self.selfTests[test]()
  File "C:/dev/SN/Slicer-build/lib/Slicer-4.4/qt-scripted-modules/DataProbe.py", line 46, in runTest
tester.runTest()
  File "C:/dev/SN/Slicer-build/lib/Slicer-4.4/qt-scripted-modules/DataProbe.py", line 611, in runTest
self.test_DataProbe1()
  File "C:/dev/SN/Slicer-build/lib/Slicer-4.4/qt-scripted-modules/DataProbe.py", line 637, in test_DataProbe1
if not os.path.exists(filePath) or os.stat(filePath).st_size == 0:
NameError: global name 'os' is not defined

From: Max Smolens <max.smolens@kitware.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24501 3bd1e089-480b-0410-8dfb-8563597acbee