Add PYTHON_INSTALL_EXTRA_OPTIONS and --install-layout=deb
    
    Debian packages should be installed under dist-packages, not
    site-packages. Debian has patched distutils and setuptools to add a new
    flag '--install-layout'. For --with-ipaplatform=debian,
    PYTHON_INSTALL_EXTRA_OPTIONS is set to '--install-layout=deb'.
    
    https://pagure.io/freeipa/issue/6764
    
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Timo Aaltonen <tjaalton@debian.org>
    Reviewed-By: Martin Basti <mbasti@redhat.com>