Pass in the kernel package late

This allows us to modify it with versions fetched during build
that we don't know upfront.

build-image

@@ -81,6 +81,7 @@ want_qcow2=
 apt_sources=
 debootstrap_dist=
 kernel_deb=
+custom_package_opt=
 
 while getopts ":hb:d:T:B" opt; do
   case ${opt} in
@@ -138,10 +139,13 @@ if [ "${build_type}" == "latest" ]; then
 	fi
 	kernel_deb="$deb"
     done
+    [ -n "${kernel_deb}" ] || { echo "No kernel found."; exit 1; }
+    custom_package_opt=(--custom-package "${kernel_deb}")
 else
     kernel_url=https://storage.puri.sm/librem5/binaries/${build_type}/latest/files/
     if [ -n "${kernel_deb}" ] && [ ! -f "files/${kernel_deb}" ]; then
 	wget -Pfiles/ "${kernel_url}/${kernel_deb}"
+	custom_package_opt=(--custom-package "files/${kernel_deb}")
     fi
 
     if [ -n "${uboot_bin}" ] && [ ! -f "files/uboot-${uboot_type}/${uboot_bin}" ]; then
@@ -157,6 +161,7 @@ echo "Using kernel ${kernel_deb}"
 escaped_apt_sources=$(echo "${apt_sources}" | sed 's/$/|/g')
 
 set -x
+# shellcheck disable=SC2086
 sudo pureos_board="${pureos_board}" \
      distro="${distro}" \
      packages="${packages}" \
@@ -177,6 +182,7 @@ sudo pureos_board="${pureos_board}" \
     --root-password='root' --hostname='pureos' --user=purism/123456 --sudo \
     --customize "${cwd}/root.sh" \
     --owner "$(whoami)" \
+    "${custom_package_opt[@]}" \
     "${vmdebootstrap_opts[@]}" \
     ${NULL}
 set +x

conf/board

@@ -21,7 +21,6 @@ case ${pureos_board} in
                         --bootsize 200M
                         --boottype ext2
                         --bootoffset 1M
-                        --custom-package "files/${kernel_deb}"
                         --no-kernel
                         --no-update-initramfs
                         --arch="${arch}"
@@ -43,7 +42,6 @@ case ${pureos_board} in
                         --bootsize 200M
                         --boottype ext2
                         --bootoffset 5M
-                        --custom-package "files/${kernel_deb}"
                         --no-kernel
                         --no-update-initramfs
                         --arch="${arch}"
@@ -63,7 +61,6 @@ case ${pureos_board} in
                         --bootsize 200M
                         --boottype ext2
                         --bootoffset 5MiB
-                        --custom-package "files/${kernel_deb}"
                         --no-kernel
                         --no-update-initramfs
                         --arch="${arch}"
@@ -85,7 +82,6 @@ case ${pureos_board} in
                         --bootsize 200M
                         --boottype ext2
                         --bootoffset 5MiB
-                        --custom-package "files/${kernel_deb}"
                         --no-kernel
                         --arch="${arch}"
                        )