gerrit_util: Slightly modify retry backoff behavior
gerrit_util: Slightly modify retry backoff behavior

This is a bandaid (over Gerrit's replication lag), but hopefully
this will increase the likelihood of success and improve the
messaging around retries at the same time.

R=tandrii

Bug: 792679
Change-Id: Ia6e3133cc23ea9b2abfeacc05750c002f8804e8b
Reviewed-on: https://chromium-review.googlesource.com/812564
Commit-Queue: Aaron Gable <bbed39beedae4cdb499af742d2fcd6c63934d93b@chromium.org>
Reviewed-by: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools