utils/scanpypi: fix buildutils check in python3

The message attribute does not exist in python3, see PEP-0352:
https://www.python.org/dev/peps/pep-0352/

Fixes:
Traceback (most recent call last):
  File "utils/scanpypi", line 743, in <module>
    main()
  File "utils/scanpypi", line 693, in main
    if 'buildutils' in err.message:
AttributeError: 'ImportError' object has no attribute 'message'

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit c3029878c5efa28eff793405095fe64327c15ad5)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

utils/scanpypi

@@ -690,7 +690,7 @@ def main():
             try:
                 package.load_setup()
             except ImportError as err:
-                if 'buildutils' in err.message:
+                if 'buildutils' in str(err):
                     print('This package needs buildutils')
                 else:
                     raise