dockertest.environment: Add support for INI config parser

Hi @cevich, I finished the INI config parser. Please let me know what tweaks do you require. I believe it can live inside even with duplicate config sections for now. Those sections will disappear once we update all the docstrings.

One more think I don't know why you choose this complex way of generating documentation using classmethods. I don't see the benefit of using, only more complex (error prone, hard to debug and hard to modify) structure and slower execution. I hope you had a good reason for that, otherwise it would be nice to modify it into 2 classes, one which represents the whole section and second one which represents each subtest.

Anyway that's just my point of view so if there is a good reason for cls, than let it be cls.

Regards,
Lukáš
Same thing here, much better to just return ``rendered`` and make ``default_configs`` into a property or a separate method.