deployment.sh: re-add mkswap command

For whatever reason the swap partition isn't enabled by default
anymore. Used to work in all my previous test runs (which
confused me already - haha), I've no idea why it's failing now
again. So re-add the mkswap command so we can at least release
2.4.1 now. Meh… ☠

From: Michael Prokop <mprokop@sipwise.com>

deployment.sh

@@ -614,6 +614,10 @@ parted -s /dev/${DISK} 'mkpart primary ext4 2048s 95%'
 parted -s /dev/${DISK} 'mkpart primary linux-swap 95% -1'
 sync
 
+SWAP_PARTITION="/dev/${DISK}2"
+echo "Initialising swap partition $SWAP_PARTITION"
+mkswap "$SWAP_PARTITION"
+
 # otherwise e2fsck fails with "need terminal for interactive repairs"
 echo FSCK=no >>/etc/debootstrap/config