Cache images inside the archive dir, rather than at the top of the tree.

Currently all of our UpdateTestArtifacts steps store images in
~/trunk/latest_image, rather than under the separate archive dirs
created for each image. Don't do that.

BUG=chromium:362106
TEST=Trybot run.

Change-Id: I123b6619957182c042c0cc62bf1ef6f186f37404
Reviewed-on: https://chromium-review.googlesource.com/194112
Reviewed-by: Yu-Ju Hong <yjhong@chromium.org>
Tested-by: David James <davidjames@chromium.org>
1 file changed