TriBITS Python scripts do not work on some modern Linux distributions

[sebrowne]

As per https://peps.python.org/pep-0394, python may not exist on some modern Linux operating systems. The particular one in question here is RHEL8. If you install one of the python3 packages, you do get python3, but not python. As per the PEP, I think it wise to discontinue use of python, given the end-of-life of Python 2.

This specifically applies to the use of the #!/usr/bin/env python idiom present in many of the TriBITS Python scripts. This is causing issues for the Trilinos AutoTester on RHEL8.