Python3 migration

[sej7278]

Fixes #542

[tuna-f1sh]

Following the discussions in #542 regarding not using macOS system Python, I've done what I suggested and added a python resolution to Common.mk. It is then pre-appended to the ard-reset-arduino scripts.

tuna-f1sh@87d5241

I've merged your changes for Python 3 support too so looks like we finally have fix?!

tuna-f1sh@3241c40

[sej7278]

yeah i quite like the PYTHON_CMD, as the way its going we're likely to need to set it for macos, i'm not entirely keen on basically ignoring the shebang on linux, but at this point i've given up a bit!

i was thinking alternatively to just patching the shebang to /usr/bin/python3 as part of debian/fedora packaging and defaulting to /usr/bin/env python

[tuna-f1sh]

I considered this too. I guess the problem with this approach is people using the repository clone.

[happyaron]

If I understand correctly, /usr/bin/env python will eventually return python3 when the migration is complete at the distro's PoV, so this imposes the program supports both python2/3 and would like to use distro's default.

[tuna-f1sh]

@happyaron if only it were that simple: see #542 (comment); /usr/bin/env python is not allowed in rpm/deb packages, they must be absolute.

[sej7278]

so if we use /usr/bin/env python and then just patch it when we build rpm/deb packages, will that work with the various macos implementations?

it'll still work on linux without hardcoding the shebang (git checkout) too.

[tuna-f1sh]

Yes, I think that is actually the simplist/best solution.

[sej7278]

ok done - reset to using env python by default and added a sed to the rpm specfile.

will have to think about the debian patch but that's outside of this repo anyway.