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/status.sh

@@ -12,14 +12,14 @@ echo "network $IMAGING_NET: $n"
 if net_active "$IMAGING_NET"; then
     (assert_imaging_isolated && echo "  isolation: OK (no forward, no ip, no host IPv4, only vnet ports)")
 fi
-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" "$CLIENT3_DISK_VOL"; do
     if vol_exists "$v"; then
         echo "volume $v: $(virsh vol-info --pool "$POOL" "$v" | awk '/Capacity|Allocation/{printf "%s %s %s  ", $1, $2, $3}')"
     else
         echo "volume $v: absent"
     fi
 done
-for vm in "$SERVER_VM" "$CLIENT_VM" "$CLIENT2_VM"; do
+for vm in "$SERVER_VM" "${ALL_CLIENTS[@]}"; do
     if dom_exists "$vm"; then
         echo "domain $vm: $(dom_state "$vm")"
         virsh domiflist "$vm" | tail -n +3 | grep -v '^$' | sed 's/^/    /'