Systemd config files were moved from /etc to /usr/lib/systemd,
so this snippet fails. Instead of editing the config file, just create
a drop-in snippet with the desired configuration.
Backported from lorax commit f38bddac3f44dc36ba5f96d997a533bbcacd6458
Signed-off-by: Stephen Gallagher <sgallagh@redhat.com>