Suggest deprecate the use of python2 except for case build

[serbinsh]

I am attempting to get OLMT running in a container and discovered that a lot, or all, of the functions that run without touching cime still use python not python3. Given the lack of p2 support and challenges with getting libs running, I would suggest switching all functions to python3 compliant except for those that run the case build in cime which still depends on python2.

Granted i suspect given the amount of code and loops this may not be an easy task!