jjb: temporary fix for python layout on deb12

jjb: temporary fix for python layout on deb12

Revert the change to 'DEB_PYTHON_INSTALL_LAYOUT=deb' which also changes
'site-packages' to 'dist-packages' which is debian specific.

Instead, temporarily add the incorrect 'local/$LIBDIR' to the
lttng-tools PYTHONPATH while we work on a fix for the build system of
the affected projects.

Change-Id: I662295ae48973eff0864377f58c915edf9ded941
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>