Tools/scripts/update-plist.py: Updates pkg-plist

Small script using base Python to update pkg-plist based upon poudriere
error logs.

Inspired by: https://codeberg.org/tcberner/poudlist, by tcberner@. This
just uses base Python instead of C++ and flaky Boost libs, runs way
faster and requires no config file.

This is mainly intendend for simple ports and it's output should be
manually reviewed.