Allows test discovery when flake8-plugin to pytest is set to run

[mdavezac]

I've set my repo to run flake8 automatically via setup.cfg flags to pytest.
It uncovered two issues in the pytest adapter:

• item.hasattr(x) called rather than hasattr(item, x), however item may not have a hasattr method.
• also uncovered a path where the testfunc variable is never defined.

For #

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• Has a news entry file (remember to thank yourself!)
• Appropriate comments and documentation strings in the code
• Has sufficient logging.
• Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated
• Test plan is updated as appropriate
• package-lock.json has been regenerated by running npm install (if dependencies have changed)
• The wiki is updated with any design decisions/details.

[msftclas]

All CLA requirements met.

[brettcannon]

I just wanted to say a quick "thanks" for the PR, @mdavezac , and we plan to try and get to this early next week.

[brettcannon]

@mdavezac Quick update: basically PyCon and a week-long event at Microsoft ate up the team's time more than we expected. And now @ericsnowcurrently is out until next week, so it's still going to be a little while until we get to this. I apologize for the delay.

[ericsnowcurrently]

Thanks again for the PR, @mdavezac. We have another PR (#5648) that fixes this in a slightly different way, along with a bunch of other small fixes.