Use ubuntu-image from a snap (candidate for now). Only build raspi images with ubuntu-image 3.0 for now.

debian/control

@@ -37,7 +37,6 @@ Depends: ${misc:Depends},
          snapd (>= 2.39) [!i386],
          squashfs-tools (>= 1:3.3-1),
          sudo,
-         ubuntu-image [!i386 !riscv64],
          python3-vmdkstream [amd64 i386],
          xz-utils,
          zerofree

live-build/auto/build

@@ -90,6 +90,7 @@ if [ "${IMAGEFORMAT:-}" = "ubuntu-image" ]; then
 	# Use ubuntu-image instead of live-build
 
 	export SNAPPY_STORE_NO_CDN=1
+	snap install --classic --channel=candidate/latest ubuntu-image
 
 	# TODO: eventually, this should be handled by a single ubuntu-image
 	#  call without having to do a conditional on ubuntu-core/classic.

live-build/auto/config

@@ -334,9 +334,8 @@ if [ -z "${IMAGEFORMAT:-}" ]; then
 	case $PROJECT:${SUBPROJECT:-} in
 		ubuntu-cpc:*|ubuntu:desktop-preinstalled|ubuntu-wsl:*)
 			case $ARCH+${SUBARCH:-} in
-				*+raspi|riscv64+?*)
-					# All raspi and RISC-V images that *have* a SUBARCH will now
-					# use ubuntu-image.
+				*+raspi)
+					# All raspi images use ubuntu-image.
 					IMAGEFORMAT=ubuntu-image
 					;;
 				*)