Faster shopfloor-setup sync, prompt spacing, XP-era test client

- Deploy shopfloor-setup with rsync instead of the copy module: the
  ~4 GB tree took about 4 minutes on every re-run because copy checksums
  each file. rsync transfers only changes; changed only when it did.
- iPXE drops a trailing space, so 'Machine number:' ran into the typed
  digits. The space now comes from a hex 20 setting.
- tests/vm: pxetest-xp is a permanent client (SeaBIOS, qemu32 32-bit CPU,
  rtl8139, 1 GiB, IDE disk) for the i686 Clonezilla path; start.sh xp.
  Only one client may run at a time across all three.

tests/vm/destroy.sh

@@ -5,13 +5,13 @@
 # Usage: tests/vm/destroy.sh
 source "$(dirname "$0")/common.sh"
 
-for vm in "$CLIENT_VM" "$CLIENT2_VM" "$SERVER_VM"; do
+for vm in "${ALL_CLIENTS[@]}" "$SERVER_VM"; do
     dom_exists "$vm" || continue
     [ "$(dom_state "$vm")" = "shut off" ] || virsh destroy "$vm" >/dev/null
     virsh undefine "$vm" --nvram >/dev/null
     log "undefined $vm"
 done
-for v in "$SERVER_DISK_VOL" "$USB_VOL" "$CLIENT_DISK_VOL" "$CLIENT2_DISK_VOL"; do
+for v in "$SERVER_DISK_VOL" "$USB_VOL" "$CLIENT_DISK_VOL" "$CLIENT2_DISK_VOL" "$CLIENT3_DISK_VOL"; do
     vol_exists "$v" || continue
     virsh vol-delete --pool "$POOL" "$v" >/dev/null
     log "deleted volume $v"