I'm not saying this is why bot_update is failing, but I never trust python threads, especially not at scale. I also think the new implementation is easier to understand and less likely to have subtle mistakes if it is extended later

Change-Id: I29be55594a400fda845ea31893789104373fd0f6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2892185Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Anthony Polito <apolito@google.com>