Use a consistent, standard directory for Python packages
We used to ship our own Python packages in /usr/local/lib/python3. This is a non-standard Python directory, which has caused issues before. It also caused issues when I tried to move tailslib there in #16935 (closed), which I moved it to /usr/lib/python3 instead.
This change has now been merged into devel, which means that currently we put Python packages into different directories for no apparent reason. I suggest that we move all of them to /usr/lib/python3.
Feature Branch: bugfix/17082-use-consistent-python-packages-dir