Use python2 interpreter explicitly.
We were just using /usr/bin/python, blindly assuming that
the default python is going to be python2, which is a very
bad assumption in these modern times.
Test Plan: run any of the scap binaries on a system with python3 installed as the default python
Reviewers: mmodell, Release-Engineering-Team, thcipriani
Reviewed By: Release-Engineering-Team, thcipriani
Subscribers: dduvall, jenkins
Differential Revision: https://phabricator.wikimedia.org/D102