change the remount procedure to work directly in grml

The bootstrap starts from `/target`, which is unusual in the FHS, but
it's better to live with what's out there than the ideal world.

howto/new-machine-cymru.md

@@ -150,21 +150,21 @@ working shell in the `chroot`:
 
     cryptsetup luksOpen /dev/sda3 crypt_dev_sda3 &&
     vgchange -a y ; \
-    mount /dev/mapper/vg_ganeti-root /mnt &&
-    for fs in /run /sys /dev /proc; do mount -o bind $fs /mnt$fs; done &&
-    mount /dev/sda2 /mnt/boot &&
-    chroot /mnt /bin/bash
+    mount /dev/mapper/vg_ganeti-root /target &&
+    for fs in /run /sys /dev /proc; do mount -o bind $fs /target$fs; done &&
+    mount /dev/sda2 /target/boot &&
+    chroot /target /bin/bash
 
 This will rebuild grub:
 
-    chroot /mnt update-grub &&
-    chroot /mnt grub-install /dev/sda
+    chroot /target update-grub &&
+    chroot /target grub-install /dev/sda
 
 And this will cleanup the rest:
 
-    umount /mnt/boot &&
-    for fs in /dev /sys /run /proc; do umount /mnt$fs; done &&
-    umount /mnt &&
+    umount /target/boot &&
+    for fs in /dev /sys /run /proc; do umount /target$fs; done &&
+    umount /target &&
     vgchange -a n &&
     cryptsetup luksClose crypt_dev_sda3