Embedded distutils __init__.py imports deprecated imp module

[jfinkels]

The Python built-in module imp has been deprecated since Python 3.4. The importlib module should be used instead.

This is related to issue #555.

[stale]

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[asottile]

@gaborbernat this is still an issue -- can this get a reopen

[johnthagen]

And @gaborbernat for context/motivation, this is very important for running with -Werror from within tox. When you do that currently, if virtualenv trips DeprecationWarnings, it's challenging and a bit ugly to try to silence them from the user side.

[johnthagen]

@gaborbernat Could you also remove the wontfix label that stale bot added?