PROCTools: Make RunTier0Tests.py python 3 friendly

Alaettin Serhan Meterequested to merge
amete/athena:master-ATEAM-630 into master

This should make RunTier0Tests.py python3 friendly, while still keeping it python2 compliant. The CI should confirm the latter. The MR also cleans up a number of things flake8 complained about.

Closes ATEAM-630

cc: @wlampl @jchapman

Edited by Alaettin Serhan Mete

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