sign_official_build: support signing 'kernel' image type

BRANCH=signer
BUG=chrome-os-partner:44227
TEST='sign_official_build.sh kernel boot_devsigned.img keys boot_resigned.img'

Change-Id: I805231ef4bd4ed86b35c0d7ca2d3fe1e704caabc
Signed-off-by: David Riley <davidriley@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/294954
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed