98dracut-systemd: don't wait for root device if remote cryptsetup active

98dracut-systemd: don't wait for root device if remote cryptsetup active

This is a plain and simple hack around dependency issues between dracut
and systemd.

When using Tang-pinned LUKS root devices, we want to rely on
`systemd-cryptsetup@.service` to unlock it. However, that service only
runs `After=remote-fs-pre.target`, while `dracut-initqueue.service` has
`Before=remote-fs-pre.target` (which makes sense because we don't want
to attempt networked root devices before networking is up).

However, the rootfs-generator here wants to make sure that the root
device exists *before* exiting the initqueue via an initqueue/finished
"devexists" hook. This will never work though because by design
`systemd-cryptsetup@.service`, which unlocks the root device, won't run
until after we exit.

So we have a dependency cycle:

    initqueue -> devexists hook -> root device ->
        systemd-cryptsetup@.service -> remote-fs-pre.target -> initqueue

There's no clean way to break this. The root issue is that there's no
way right now to split sequencing of systemd services across the
initqueue/online and initqueue/finished events because it's all bundled
in a single service. (The deeper root issue of course is that we have
two init systems. :) ).

Here we do a tactical fix: if there's a `systemd-cryptsetup@.service`
instance, let's assume it's for the root device and skip waiting for it
to show up if it depends on `remote-fs-pre.target`.