Issue 50037 - lib389 fails to install in venv under non-root user
    
    Bug description:
    Some files were installed using absolute path, preventing installation
    under non-root user.
    
    Fix description:
    Change paths to be relative to the current prefix.
    Update .gitignore to exlcude venv and build products.
    Update tox.ini to the current supported Python versions.
    
    Fixes https://pagure.io/389-ds-base/issue/50037
    
    Reviewed by: mhonek, firstyear, spichugi (Thanks!)