Add random variation at the cron creation time.

[Dominic Kim <st...@gmail.com>]

Hi, Whiskers.

There is a PR[1] open to add some random delay at Cron creation time.
This can alleviate the thundering herd[2] issue.

It will add a fixed random delay based on a hash of the trigger name.
The delay would be less than 60s, so it would not violate a Cron expression
but work with some initial delays.
Since the delay is deterministically calculated, it persists across
multiple deployments.

For compatibility reasons, this feature will be disabled by default and
also configurable by OW operators.

Any comments or feedback would be appreciated.
And I would merge the PR unless there are any comments in 48 hours.


[1]: https://github.com/apache/openwhisk-package-alarms/pull/198
[2]: https://en.wikipedia.org/wiki/Thundering_herd_problem

Best regards
Dominic