Use xz -T4 -0 instead of pxz

Test showed very little difference in file-size between -0 and -9 while
both compression and decompression need much less memory and compression
needs less CPU time for -0.

Supported xz versions before 5.2 also accept the -T4 option but ignore it.

Also depend on xz-utils instead of on pxz.

LP: #1701132

debian/changelog

@@ -2,8 +2,11 @@ livecd-rootfs (2.448) UNRELEASED; urgency=medium
 
   [ Balint Reczey ]
   * Depend on packages in main instead of installing them at runtime
-  * Depend on pxz and vmdk-stream-converter instead of installing them
-    at run time
+  * Depend on vmdk-stream-converter instead of installing it at run time
+  * Use xz -T4 -0 instead of pxz (LP: #1701132)
+    Supported xz versions before 5.2 also accept the -T4 option but ignore
+    it.
+  * Depend on xz-utils instead of pxz
 
   [ Mathieu Trudel-Lapierre ]
   * auto/config: enable Debug::pkgDepCache::AutoInstall so tracking down

debian/control

@@ -25,7 +25,6 @@ Depends: ${misc:Depends},
          lzma,
          parted,
          procps,
-         pxz,
          python-minimal | python,
          python3-software-properties,
          qemu-utils,
@@ -35,6 +34,7 @@ Depends: ${misc:Depends},
          sudo,
          ubuntu-image,
          vmdk-stream-converter [amd64 i386],
+         xz-utils,
          zerofree
 Suggests: partimage
 Breaks: ubuntu-defaults-builder (<< 0.32)

live-build/auto/build

@@ -20,7 +20,7 @@ if [ "${IMAGEFORMAT:-}" = "ubuntu-image" ]; then
 	env SNAPPY_STORE_NO_CDN=1 \
 	ubuntu-image -c edge \
 		-o livecd."$PROJECT".img livecd."$PROJECT".model-assertion
-	pxz -T4 livecd."$PROJECT".img
+	xz -0 -T4 livecd."$PROJECT".img
 	exit 0
 fi
 

live-build/ubuntu-cpc/hooks/040-qcow2-image.binary

@@ -13,7 +13,7 @@ case $ARCH:$SUBARCH in
 	# Not sure if any other cloud images use subarch for something that
 	# should take qcow2 format, so only skipping this on raspi2 for now.
 	armhf:raspi2)
-		pxz -T4 -c binary/boot/disk.ext4 > livecd.ubuntu-cpc.disk1.img.xz
+		xz -0 -T4 -c binary/boot/disk.ext4 > livecd.ubuntu-cpc.disk1.img.xz
 	        exit 0
 		;;
 esac