For the IMAGEFORMAT=none parts to work for ubuntu-image classic builds, we need to make sure IMAGEFORMAT is preserved and not overwritten if defined. Backporting from trunk.

debian/changelog

@@ -1,3 +1,11 @@
+livecd-rootfs (2.408.24) UNRELEASED; urgency=medium
+
+  * For the IMAGEFORMAT=none parts to work for ubuntu-image classic builds, we
+    need to make sure IMAGEFORMAT is preserved and not overwritten if defined.
+    Backporting from artful.
+
+ -- Łukasz 'sil2100' Zemczak <lukasz.zemczak@ubuntu.com>  Tue, 21 Nov 2017 17:01:14 +0100
+
 livecd-rootfs (2.408.23) xenial; urgency=medium
 
   [ Gary Wang ]

live-build/auto/config

@@ -107,11 +107,13 @@ add_binary_hook ()
 	BINARY_HOOKS="${BINARY_HOOKS:+$BINARY_HOOKS }$1"
 }
 
-case $PROJECT in
-	ubuntu-cpc)
-		IMAGEFORMAT=ext4
-		;;
-esac
+if [ -z "${IMAGEFORMAT:-}" ]; then
+	case $PROJECT in
+		ubuntu-cpc)
+			IMAGEFORMAT=ext4
+			;;
+	esac
+fi
 
 case $IMAGEFORMAT in
 	ext2|ext3|ext4)