Switch Python Doxygen unit tests to use inspect.getdoc()

Using the standard inspect module instead of accessing __doc__ directly allows
the tests to pass both when using and not using -builtin, as whitespace-only
differences between the docstrings don't matter then because inspect.getdoc()
removes the indentation and the leading and trailing spaces.

This is similar to what had been already done for python_docstring unit test
in fa282b3540.

Examples/test-suite/python/doxygen_ignore_runme.py

@@ -1,20 +1,19 @@
 #!/usr/bin/python
 
 import doxygen_ignore
+import inspect
 import commentVerifier
 
-commentVerifier.check(doxygen_ignore.func.__doc__,
-    r"""
-    A contrived example of ignoring too many commands in one comment.
+commentVerifier.check(inspect.getdoc(doxygen_ignore.func),
+    """\
+A contrived example of ignoring too many commands in one comment.
 
 
 
 
 
 
-    This is specific to **Python**.
+This is specific to **Python**.
 
 
-    Command ignored, but anything here is still included.
-
-    """)
+Command ignored, but anything here is still included.""")