dracut: Don't prompt twice upon reaching a dracut breakpoint
dracut: Don't prompt twice upon reaching a dracut breakpoint

When invoking a dracut breakpoint, emergency hooks are run twice: once
from their dedicated unit (e.g. dracut-pre-pivot.service ->
/usr/bin/dracut-pre-pivot) and once from the dracut emergency unit
(dracut-emergency.service -> /usr/bin/dracut-emergency). Set a flag file
in the initramfs to avoid prompting twice.

coreos/ignition,coreos/ignition,coreos/bootengine,coreos/ignition