Migrate python-boto to cloud team maintainership

This MR encompasses 4 primary changes:

1. Incorporate zigo's NMU dropping python2 support, which was never committed to git.
2. Sets the cloud-team as maintainer of the package, with Uploaders == noahm and zigo (we've made recent uploads; others are welcome to contribute, of course)
3. Convert to 3.0 (quilt) source format from previous 1.0 format. (I resisted the urge to blow away pristine-tar; we are still using that for now.)
4. Fix python 3.8 compatibility issues, notably 953970

Once this is merged and uploaded, we should be sure to break the fork relationship with the original repo, which isn't something I have authorization to do.