Change all VM update tests to update to vm image (not non-vm image).

We have some tests now that will need to ensure that we update to the
vm image instead of the non-vm image.

I've had to make more changes to au_test_harness than originally expected
because of some ugly built-in assumptions I've cleaned up.

BUG=chromium:314970
TEST=Remote trybot.

Change-Id: I32f5a8e9a9062e79b787f630a71dafaa27a4215f
Reviewed-on: https://chromium-review.googlesource.com/174793
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Chris Sosa <sosa@chromium.org>
Tested-by: Chris Sosa <sosa@chromium.org>
5 files changed