Produce buildd kernel and initrd as separate artifacts

Multipass on Mac OS X requires standalone kernel and initrd artifacts
to boot.

Also call update-initramfs on all installed kernels. We only have one
kernel installed, so we don't need to specify an explicit version.

debian/changelog

@@ -1,3 +1,12 @@
+livecd-rootfs (2.665) UNRELEASED; urgency=medium
+
+  * buildd: produce kernel and initrd as separate artifacts
+  * buildd: call update-initramfs for all installed kernels
+    We only have one kernel installed, so we don't need to
+    specify an explicit version.
+
+ -- David Krauser <david.krauser@canonical.com>  Tue, 20 Oct 2020 15:00:38 -0400
+
 livecd-rootfs (2.664.10) focal; urgency=medium
 
   * Do not hard-code the UC20 amd64 image size to 8GB as now ubuntu-image

live-build/buildd/hooks/52-linux-virtual-image.binary

@@ -56,8 +56,11 @@ chroot "$mount_d" update-grub
 undivert_grub "$mount_d"
 
 # Update initramfs image
-chroot "$mount_d" \
-    sh -c 'update-initramfs -c -v -k $(ls /boot/vmlinuz*generic | sed 1q | cut -d- -f2-3)'
+chroot "$mount_d" update-initramfs -c -v -k all
+
+# extract kernel and initrd
+cp $mount_d/boot/initrd.img-* livecd.$PROJECT.initrd-generic
+cp $mount_d/boot/vmlinuz-* livecd.$PROJECT.vmlinuz-generic
 
 # Cleanup
 env DEBIAN_FRONTEND=noninteractive chroot "$mount_d" apt-get \