pmconfig.py: properly handle invalid regex
pmconfig.py: properly handle invalid regex

Fail hard on invalid regex patters to avoid silent surprises.
QA to follow, using the "challenging values" archive.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp