Job ALREADY_EXISTS in post commit

I noticed a job failed with ALREDY_EXISTS error, a sign of same `job_name` auto generated twice. Could we add a 1 second delay to prevent things like this?

https://builds.apache.org/view/Beam/job/beam_PostCommit_Python_Verify/1877/consoleFull

cc: [~pabloem] Another perspective, would it make sense to add a small random component (e.g. 1-2 digits) to job name to reduce this issue? Or perhaps include ms resolution.

Imported from Jira [BEAM-1986](https://issues.apache.org/jira/browse/BEAM-1986). Original Jira may contain additional context.
Reported by: altay.

Start with the Apache Beam post-commit configuration behind the linked beam_PostCommit_Python_Verify build and trace how job_name is generated. Compare the duplicate-job failure in the linked console output with the available naming logic; done means reproducing the collision and agreeing on a tested prevention strategy.

Written by the indexing model from the issue text.