gs_cache: fall back to service account when default auth fails

BUG=b:179721419
TEST=manually tested on chromeos2-devservertest

Change-Id: I1528d4ee7e9e68400a5b0011174e6a9e3053d5f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2690206
Commit-Queue: Congbin Guo <guocb@chromium.org>
Tested-by: Congbin Guo <guocb@chromium.org>
Auto-Submit: Congbin Guo <guocb@chromium.org>
Reviewed-by: Allen Li <ayatane@chromium.org>
1 file changed