Add exponential backoff to bot_update.

Add exponential backoff to bot_update.

BUG=513560
R=agable@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=296102

[ghost stip (do not use), 2015-07-24 02:33:12]

stip@chromium.org changed reviewers:
+ hinoka@chromium.org, tandrii@chromium.org

[ghost stip (do not use), 2015-07-24 02:33:13]

ptal

[agable, 2015-07-24 02:37:21]

agable@chromium.org changed reviewers:
+ agable@chromium.org

[agable, 2015-07-24 02:37:22]

https://codereview.chromium.org/1254753002/diff/1/scripts/slave/bot_update.py
File scripts/slave/bot_update.py (right):

https://codereview.chromium.org/1254753002/diff/1/scripts/slave/bot_update.py...
scripts/slave/bot_update.py:418: if attempt > 0:
attempt is always > 0, it starts at 1. I think you want "if result == RETRY:"

https://codereview.chromium.org/1254753002/diff/1/scripts/slave/bot_update.py...
scripts/slave/bot_update.py:419: sleep_time = 4 ** attempt
jitter by +/- 20%?

[ghost stip (do not use), 2015-07-24 02:48:02]

ptal

[agable, 2015-07-24 02:48:17]

LGTM with a safety nit.

https://codereview.chromium.org/1254753002/diff/2/scripts/slave/bot_update.py
File scripts/slave/bot_update.py (right):

https://codereview.chromium.org/1254753002/diff/2/scripts/slave/bot_update.py...
scripts/slave/bot_update.py:422: print '===backing off, sleeping for %ds===' %
sleep_time
I'm scared that "%ds" is a format thing. Maybe do "%d secs" just to be same, and
to match "%.1f mins" above.

[ghost stip (do not use), 2015-07-24 02:50:16]

https://codereview.chromium.org/1254753002/diff/2/scripts/slave/bot_update.py
File scripts/slave/bot_update.py (right):

https://codereview.chromium.org/1254753002/diff/2/scripts/slave/bot_update.py...
scripts/slave/bot_update.py:422: print '===backing off, sleeping for %ds===' %
sleep_time
On 2015/07/24 at 02:48:17, agable wrote:
> I'm scared that "%ds" is a format thing. Maybe do "%d secs" just to be same,
and to match "%.1f mins" above.

done

[ghost stip (do not use), 2015-07-24 03:34:40]

The CQ bit was checked by stip@chromium.org

[ghost stip (do not use), 2015-07-24 03:34:40]

The patchset sent to the CQ was uploaded after l-g-t-m from agable@chromium.org
Link to the patchset: https://codereview.chromium.org/1254753002/#ps30001
(title: "Address final nit.")

[ghost stip (do not use), 2015-07-24 03:35:34]

Committed patchset #3 (id:30001) manually as 296102.