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.
Instead of injecting an empty resolv.conf with an includes.chroot, we'll
inject it in late with a hook. The empty resolv.conf breaks DNS early in
the build, and causes some binary hooks to fail.
