Update trigger_wait_ac_task.py to use GCS instead of webhooks

* Add more frequent task status updates.
* Add exponential retries when hitting GCS.

Bug: skia:8087
Bug: skia:8387
Change-Id: Iff8320b88999fde53c1ad4814dc9243ebd8138a8
Reviewed-on: https://skia-review.googlesource.com/155163
Commit-Queue: Ravi Mistry <rmistry@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
1 file changed