system-tests: fix module removal during cleanup

system-tests: fix module removal during cleanup

Currently, cleanup files for system tests will look like this:

modprobe -q -r vport_vxlan
modprobe -q -r vport_sttmodprobe
modprobe -q -r vport_lispmodprobe
modprobe -q -r vport_gremodprobe
modprobe -q -r vport_genevemodprobe
modprobe -r openvswitch

This is caused by a missing newline in m4_foreach EXPRESSION and the fact that
on_exit is a shell function. It was being expanded like this:

on_exit 'modprobe -q -r vport_genevemodprobe' -q vport_gre

Fixes: 53eb8cb83013 ("tests: Replace ON_EXIT m4 macro by on_exit() shell function.")
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@redhat.com>
Signed-off-by: Joe Stringer <joe@ovn.org>