units: add umount unit files for Debian

Add unit files to call

/etc/init.d/umountnfs.sh stop (network file systems)
/etc/init.d/umountfs stop     (local file systems)
/etc/init.d/umountroot stop   ("/" file system)

in the right order and hook them up in the umount.target so they are run
on shutdown and reboot.

units/debian/umountfs.service

@@ -0,0 +1,18 @@
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU General Public License as published by
+#  the Free Software Foundation; either version 2 of the License, or
+#  (at your option) any later version.
+
+[Unit]
+Description=Turn off swap and umount all local file systems
+DefaultDependencies=no
+After=killall.service
+Before=reboot.service poweroff.service halt.service umountroot.service
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/etc/init.d/umountfs stop
+StandardOutput=tty

units/debian/umountnfs.service

@@ -0,0 +1,18 @@
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU General Public License as published by
+#  the Free Software Foundation; either version 2 of the License, or
+#  (at your option) any later version.
+
+[Unit]
+Description=Umount all network file systems
+DefaultDependencies=no
+After=killall.service
+Before=reboot.service poweroff.service halt.service umountfs.service
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/etc/init.d/umountnfs.sh stop
+StandardOutput=tty

units/debian/umountroot.service

@@ -0,0 +1,18 @@
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU General Public License as published by
+#  the Free Software Foundation; either version 2 of the License, or
+#  (at your option) any later version.
+
+[Unit]
+Description=Mount the root file system read-only
+DefaultDependencies=no
+After=killall.service
+Before=reboot.service poweroff.service halt.service
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/etc/init.d/umountroot stop
+StandardOutput=tty