patchwork-tools: invoke python3 from scripts

Due to the fact that development was done in a python3
native environment, it wasn't apparent that the userspace
scripts needed to be updated to specify python3.

This change removes any chance for python2 to be called
as the interpreter for any of those scripts.

Change-Id: I6547f64f0de288dbfe94db3333d3b79199d2f9de
14 files changed