- Enable instantiated services (boo#1184165)

- Prepare instantiated service/timer support but not enable it:
This seems to fail due to missing systemd support right now.
So the only option at the moment is to copy the timer and unit
file for a 2nd instance. Mark all files as part of dehydrated.target

- Rework support for /etc/dehydrated/postrun-hooks.d/:
dehydrated.service nolonger starts them directly, the support was
moved to a separate unit file. Please run:
systemctl enable dehydrated-postrun-hooks.service
to restore this functionality
- Run dehydrated as dehydrated user again (forwarded request 882188 from darix)