bigfile/py/test_basic: Rework exception testing codepath so it is active on py3 also

As comments being removed states "on python3 exception state is cleared
upon exiting from `except`" - so let's move exc_* fetching under except
clause - this way we'll get correct exception objects on both py2 and py3.

bigfile/tests/test_basic.py

@@ -132,15 +132,10 @@ def test_pagefault_savestate():
             # state, and say we are done ok
             try:
                 1/0
-            except ZeroDivisionError:
-                pass
-
+            except:
                 exc_type, exc_value, exc_traceback = sys.exc_info()
-            if PY2:
+
             assert exc_type is ZeroDivisionError
-            else:
-                # on python3 exception state is cleared upon exiting from `except`
-                assert exc_type is None
 
 
             # NOTE there is a loop created here: