image_signing: sign_official_build.sh: convert to info/error helpers

This makes the output easier to follow when multiple scripts are being run.

BRANCH=None
BUG=chromium:714598
TEST=signing images still works

Change-Id: I4097fd58f349dc84c242dd12d6a94e12f387a1f0
Reviewed-on: https://chromium-review.googlesource.com/498232
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: David Riley <davidriley@chromium.org>
1 file changed