Use --reflink=always when copying the fallback initramfs

It saves us ~20MB.

build-inside-vm.sh

@@ -92,7 +92,7 @@ function image_cleanup() {
   # So for the initial install we use the fallback initramfs, and
   # "autodetect" should add the relevant modules to the initramfs when
   # the user updates the kernel.
-  cp -a "${MOUNT}/boot/"{initramfs-linux-fallback.img,initramfs-linux.img}
+  cp --reflink=always -a "${MOUNT}/boot/"{initramfs-linux-fallback.img,initramfs-linux.img}
 
   sync -f "${MOUNT}/etc/os-release"
   fstrim --verbose "${MOUNT}"