Even trivial service occasionally get stuck, for example when
there's a problem with the journal. There's nothing more annoying
that looking at the cylon eye for a job with an infinite timeout.
Use standard 90s for jobs that do some work, and 30s for those which
should be almost instantenous.
The unit file only active the machine-id-commit helper if /etc is mounted
writable and /etc/machine-id is an independant mount point (should be a tmpfs).