Like other distros, openSUSE Tumbleweed recently changed libexecdir from
/usr/lib to /usr/libexec. Add it as an allowed path for libxl-save-helper
and pygrub.
Signed-off-by: Jim Fehlig <jfehlig@suse.com> Reviewed-by: Neal Gompa <ngompa13@gmail.com> Reviewed-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>