Fix timeout when using XCom with KubernetesPodOperator

[dimberman]

Currently, the xcom sidecar container for the KubernetesPodOperator will
sleep for 30 seconds before checking if the xcom has completed. This is
far too long of a wait, as a 1 second wait will ensure that the process
is not consistently blocked.

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[andrewgodwin]

Daniel and I did a lot of diving into this to work out why it was 30 seconds to begin with, and my conclusion is that when this was ported from Python to Bash, it was converted from a try/except to a trap, but without the realisation that trap will wait for the sleep to finish before it runs the interrupt command - meaning it will always wait up to 30 seconds to return. The Python version would not have had this issue, so that's why it had 30 seconds in there to start with.

I think this change looks good based on what I researched.

[github-actions]

The PR is likely OK to be merged with just subset of tests for default Python and Database versions without running the full matrix of tests, because it does not modify the core of Airflow. If the committers decide that the full tests matrix is needed, they will add the label 'full tests needed'. Then you should rebase to the latest master or amend the last commit of the PR, and push it with --force-with-lease.