image_signing: sign_official_build.sh: switch verification to loopbacks

Rather than copy out the rootfs to a temp file and perform checks on that,
run the checks directly on the image.  This saves us from having to copy
many GB worth of data which can be expensive on the VMs (slow disk I/O).

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

Change-Id: Ie7d1c432aacb69e57b6c5fd9ab810b8d0b054860
Reviewed-on: https://chromium-review.googlesource.com/505476
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: David Riley <davidriley@chromium.org>
1 file changed