[roll] Retry tag push if it fails after 30s

This is still somewhat unreliable but makes it even less likely that GoB
replication delays will affect the second push.

b/169389802

Change-Id: I18a32bf30b4e89960f576c74f16aa41c270591b1
Reviewed-on: https://dart-review.googlesource.com/c/recipes/+/167582
Commit-Queue: Alexander Thomas <athom@google.com>
Auto-Submit: Alexander Thomas <athom@google.com>
Reviewed-by: William Hesse <whesse@google.com>
3 files changed