image_test: Check for the correct chrome binaries

chromeos-chrome installs binaries depending on these two USE flags:
app_shell and envoy. This CL checks for the correct binary.

BUG=chromium:530765
TEST=trybot on envoy-jerry, veyron_rialto, and generic-x86

Change-Id: Ica66b898fe0d659c1ba0a6f47456558836c4e72a
Reviewed-on: https://chromium-review.googlesource.com/299550
Commit-Ready: Nam Nguyen <namnguyen@chromium.org>
Tested-by: Nam Nguyen <namnguyen@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed