gs_cache: telemetry wrapper fixes

1. Use a file lock instead of in-memory lock to lock among processes.
2. Fix a performance issue when download files to a local temp dir.

BUG=chromium:1087989
TEST=tested on chromeos2-devserver6 by calling /setup_telemetry multiple times
  simultaneously and monitor the performance.
  for ((i=0;i<24; i++));do curl http://localhost:8888/setup_telemetry?archive_url=gs://chromeos-image-archive/banjo-release/R85-13310.35.0 & done

Change-Id: Ief90fb39181b00106f913d14adaf29bf76366b88
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2333390
Tested-by: Congbin Guo <guocb@chromium.org>
Auto-Submit: Congbin Guo <guocb@chromium.org>
Reviewed-by: Sanika Kulkarni <sanikak@chromium.org>
1 file changed