Instead of logging warnings we now rethrow exceptions thrown inside
scheduled/submitted tasks. This will still log them as warnings in
production but has the added benefit that if they are thrown during
unit/integration test runs, the test will be flagged as an error.
This is a continuation of #38014
Fixed NPE that caused CCR tests (IndexFollowingIT and likely others)
to fail.
schedule could bubble rejected exception to uncaught exception
handler when not using SAME executor if thread pool is terminated.
Now ignore rejected exception silently if executor is shutdown.
20c66c5a05