emerges chromeos-test-root in test_image_util.sh

After crosreview.com/177426 and crosreview.com/177409 land,
chromeos-test-root will be able to do both the following work
1) add additional upstart jobs (chromeos-base/chromeos-test-init)
2) install test ssh key to /root/.ssh/authorized_keys
   (chromeos-test-testauthkeys)

This cl makes test_image_util.sh emerge chromeos-test-root
The next step following this cl is to remove
the old 350addTestAuthKeys script that was used to add ssh keys.

CQ-DEPEND=I99fb7916a2c0c15b8c47e18893c882ca086d0d24
TEST=1) Pick the changes from crosreview.com/177426
and crosreview.com/177409, build a lumpy test image, confirmed
that the image works and we can ssh to it as root without password.
2) Manually removed 350addTestAuthKeys, repeat 1)

BUG=chromium:306619

Change-Id: If5dd6d6b524b82b3adfdc7ccd50083c738cb415e
Reviewed-on: https://chromium-review.googlesource.com/177451
Reviewed-by: Richard Barnette <jrbarnette@chromium.org>
Commit-Queue: Fang Deng <fdeng@chromium.org>
Tested-by: Fang Deng <fdeng@chromium.org>
1 file changed