[U-Boot] [PATCHv3 00/13] Moving test/py to Python 3

So, here's the third and I think final pass at moving our test/py code over to Python 3. Over v2 I've integrated reviews/test tags and integrated Stephen's changes to allow for Python 3.5 to be used still.

I do want to note that while I do understand the desire to use the distribution packages for python modules I don't think that's reproducible enough long term. That's what lead to our current pinning to pytest 2.8.7 (incompatible upstream changes) and there's just so many different versions packaged in different releaes.

I'll post the minor patches for the Docker images as well in reply to this message shortly.

Thanks again for the reviews, changes and suggestions all!