GitLab

Fixes two things in the VR auto bisect script:
1. Sets an empty list as the default for the checkout override arg, as
   otherwise it was trying to iterate over None when not set.
2. Ensure that the VR APKs are downloaded during syncing.

Change-Id: I2191accdc23fd858b0588c7772785ce4a95edc6a
Reviewed-on: https://chromium-review.googlesource.com/965115Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543534}