systemd: pre-pivot hooks runs after /sysroot is mounted

If rootflags=nofail, sysroot.mount won't strictly run "Before"
initrd-root-fs.target. So we need to order dracut-pre-pivot after
sysroot.mount.

modules.d/98systemd/dracut-pre-pivot.service

@@ -10,7 +10,7 @@
 [Unit]
 Description=dracut pre-pivot and cleanup hook
 Documentation=man:dracut-pre-pivot.service(8)
-After=initrd.target initrd-parse-etc.service
+After=initrd.target initrd-parse-etc.service sysroot.mount
 After=dracut-initqueue.service dracut-pre-mount.service dracut-mount.service
 Before=initrd-cleanup.service
 ConditionPathExists=/etc/initrd-release