GitLab

Works around two separate issues in the Gold Python code caused by
`goldctl diff` misbehaving:

1. Creates a copy of the working directory to pass to `goldctl diff`, as
   it currently clobbers the auth files in the given working directory.
2. Uses the public version of the Gold instance for `goldctl diff`, as
   authentication does not currently work for the non-public instance.

Bug: skia:10610, skia:10611, skia:10587
Change-Id: Idff3202c048f4e7baa986cfc8ad21fb918382603
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2416861
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Commit-Queue: Tibor Goldschwendt <tiborg@chromium.org>
Reviewed-by: Tibor Goldschwendt <tiborg@chromium.org>
Auto-Submit: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808197}