[issue21503] Use test_both() consistently throughout test_importlib

[Eric Snow]

Eric Snow added the comment:

FWIW, this change was motivated by the importlib backport (I found some time to work on it).  The import_importlib()/test_both() approach definitely makes backporting the tests easier (thanks for that).

BTW, thanks for also consolidating the various test_importlib util modules.  That also helped.

----------

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue21503>
_______________________________________