[OE-core] Python3 for bitbake/OE merged

[Richard Purdie]

I just watched things break on the autobuilder as trying to keep the
python3 patches in sync with all the other changes coming in was
proving tricky and not really a productive use of my time.

I've therefore merged the python3 patches and bitbake is now using
python3. If there are any further issues, we can fix in master. This
may mean some other patchsets need to rebase.

Cheers,

Richard