Currently, on soft-reboot, /run/credentials/@system is unmounted
because it has DefaultDependencies=yes and as such will have
Conflicts=umount.target and Before=umount.target. Let's make sure
credential mounts survive soft-reboot by implying DefaultDependencies=no
for credential mounts.
If a unit is running in an image and wants to survive a soft-reboot,
then it can't be deactivated by the storage of the image going away.
Relax the dependency to a Wants=. Access to the image is not needed
when the unit is running anyway, so downgrade to Wants=.
