Don't install a preexec_fn by default
ipautil.run() now only installs a preexec_fn when it is actually needed.
This addresses a compatibility issue with mod_wsgi subinterpreters under
Python 3.8.
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1759290
See: https://bugs.python.org/issue37951
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>