gen the initramfs with the right options and repack it with lzma

debian/changelog

@@ -1,4 +1,4 @@
-livecd-rootfs (2.488~ppa2) bionic; urgency=medium
+livecd-rootfs (2.488~ppa4) bionic; urgency=medium
 
   * Move casper from filesystem.squashfs to installer.squashfs. 
 

live-build/ubuntu-server/hooks/032-installer-squashfs.binary

@@ -41,7 +41,16 @@ chroot $SQUASH_ROOT apt-get update
 chroot $SQUASH_ROOT apt-get -y install user-setup
 chroot $SQUASH_ROOT apt-get -y install lupin-casper
 
-mv $SQUASH_ROOT/boot/initrd.img-* livecd.ubuntu-server.initrd-generic
+# Installing lupin-casper means we need a new initramfs, so we
+# cargo cult stuff from lb_chroot_hacks:
+chroot $SQUASH_ROOT CASPER_GENERATE_UUID=1 update-initramfs -k all -t -u
+for INITRAMFS in $(find $SQUASH_ROOT/boot -name 'initrd*' -not -type l); do
+    zcat "${INITRAMFS}" | lzma -c -6 > "${INITRAMFS}.new"
+    mv "${INITRAMFS}.new" "${INITRAMFS}"
+done
+# and lb_binary_linux-image:
+mv $SQUASH_ROOT/boot/initrd.img-* binary/casper/
+# To replace the previously built one with it.
 
 chroot $SQUASH_ROOT apt-get -y install curtin