[issue21099] Switch applicable importlib tests to use PEP 451 API

[Eric Snow]

Changes by Eric Snow <ericsnowcurrently at gmail.com>:


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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed
versions: +Python 3.6 -Python 3.4, Python 3.5

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue21099>
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