Some more changes needed for enabling official intel-iot image builds.

debian/changelog

@@ -2,8 +2,13 @@ livecd-rootfs (2.664.28) UNRELEASED; urgency=medium
 
   [ Brian Murray ]
   * Make sure we're using the 'classic' branch for the intel-iot gadget.
+    (LP: #1938338)
 
- -- Łukasz 'sil2100' Zemczak <lukasz.zemczak@ubuntu.com>  Thu, 12 Aug 2021 12:58:24 +0200
+  [ Łukasz 'sil2100' Zemczak ]
+  * Add support for passing SUBPROJECT to classic ubuntu-image calls. This
+    should fix running desktop-preinstalled builds. (LP: #1938338)
+
+ -- Łukasz 'sil2100' Zemczak <lukasz.zemczak@ubuntu.com>  Mon, 16 Aug 2021 13:02:23 +0200
 
 livecd-rootfs (2.664.27) focal; urgency=medium
 

live-build/auto/config

@@ -444,6 +444,7 @@ case $IMAGEFORMAT in
 					;;
 			esac
 
+			UBUNTU_IMAGE_ARGS="$UBUNTU_IMAGE_ARGS${SUBPROJECT:+ --subproject \"$SUBPROJECT\"}"
 			UBUNTU_IMAGE_ARGS="$UBUNTU_IMAGE_ARGS${PROPOSED:+ --with-proposed}"
 			UBUNTU_IMAGE_ARGS="$UBUNTU_IMAGE_ARGS${EXTRA_PPAS:+ --extra-ppas \"$EXTRA_PPAS\"}"