enable tests in python packages

[g-arjones]

Depends on:

• extend python package features autobuild#113

[doudou]

Does it really make sense to choose a test framework globally like this ? The Python community does not have multiple test harnesses ?

[g-arjones]

Either pytest and unittest but pytest can be used just as a runner for unittest tests (and other frameworks as well). So, AFAIK, pytest should fit most use cases.

[g-arjones]

Turns out there are limitations in using pytest as a runner for other frameworks. Since I don't have enough python experience to be sure whether these are relevant or not, I'm closing this PR. I will be glad to add it back if more experienced python people are interested.