osdep/hurd/getroot: Use "part:" qualifier

When using userland drivers such as rumpdisk, we'd rather make ext2fs use
parted-based libstore partitioning support. That can be used for kernelland
drivers as well, so we can just make GRUB always use the "part:" qualifier
to switch ext2fs to it.

grub_util_find_hurd_root_device() then has to understand this syntax and
translate it into the /dev/ entry name.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

util/grub.d/10_hurd.in

@@ -128,9 +128,11 @@ EOF
   else
       opts=
   fi
+  device=device:${GRUB_DEVICE#/dev/}
+  device=$(echo "$device" | sed -e 's/^device:\(.*[0-9]\+\)s\([0-9]\+\)$/part:\2:device:\1'/)
   sed "s/^/$submenu_indentation/" << EOF
 	echo		'$(echo "$message" | grub_quote)'
-	multiboot	${kernel} root=device:${GRUB_DEVICE#/dev/} $opts ${GRUB_CMDLINE_GNUMACH}
+	multiboot	${kernel} root=$device $opts ${GRUB_CMDLINE_GNUMACH}
 EOF
 
   if [ x$type != xrecovery ] ; then