bsdinstall/zfsboot: Skip adding swap lines to /etc/fstab if swap is 0 sized

Differential Revision:	https://reviews.freebsd.org/D2571
Reviewed by:	dim
Approved by:	eadler (mentor)
Sponsored by:	ScaleEngine Inc.

usr.sbin/bsdinstall/scripts/zfsboot

@@ -953,6 +953,8 @@ zfs_create_diskpart()
 	esac # $ZFSBOOT_PARTITION_SCHEME
 
 	# Update fstab(5)
+	local swapsize
+	f_expand_number "$ZFSBOOT_SWAP_SIZE" swapsize
 	if [ "$isswapmirror" ]; then
 		# This is not the first disk in the mirror, do nothing
 	elif [ "$ZFSBOOT_SWAP_ENCRYPTION" -a "$ZFSBOOT_SWAP_MIRROR" ]; then
@@ -972,6 +974,8 @@ zfs_create_diskpart()
 		             /dev/$disk${swappart}.eli none swap sw 0 0 \
 		             $BSDINSTALL_TMPETC/fstab ||
 		             return $FAILURE
+	elif [ ${swapsize:-0} -eq 0 ]
+		# If swap is 0 sized, don't add it to fstab
 	else
 		f_eval_catch $funcname printf "$PRINTF_FSTAB" \
 		             /dev/$disk$swappart none swap sw 0 0 \