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.

live-build/auto/config

@@ -104,6 +104,7 @@ add_binary_hook ()
 	BINARY_HOOKS="${BINARY_HOOKS:+$BINARY_HOOKS }$1"
 }
 
+if [ -z "${IMAGEFORMAT:-}" ]; then
 	case $PROJECT:$SUBPROJECT in
 		ubuntu-cpc:*)
 			IMAGEFORMAT=ext4
@@ -112,6 +113,7 @@ case $PROJECT:$SUBPROJECT in
 			IMAGEFORMAT=plain
 			;;
 	esac
+fi
 
 case $IMAGEFORMAT in
 	ext2|ext3|ext4)