Related to https://github.com/apache/airflow/issues/9655

It would be nice to add a message when you get this error with some info, like 'This probably is because a lack of RAM' or something like that. 

I have found the code where the -9 is assigned but have no idea how to add a logging message. 

        self.process = None

        if self._rc is None:
            # Something else reaped it before we had a chance, so let's just "guess" at an error code.
            self._rc = -9
tests/task/task_runner/test_standard_task_runner.py
ti = TI(task=task, execution_date=DEFAULT_DATE)
        job1 = LocalTaskJob(task_instance=ti, ignore_ti_state=True)
        session.commit()
        runner = StandardTaskRunner(job1)
        runner.start()
        
        time.sleep(3)
        pgid = os.getpgid(runner.process.pid)
        assert pgid > 0
        assert pgid != os.getpgid(0), "Task should be in a different process group to us"
        processes = list(self._procs_in_pgroup(pgid))
        runner.terminate()
        
        for _ in range(20):
            if os.path.exists(path):
                break
            time.sleep(2)
        with open(path) as f:
            assert "ON_KILL_TEST" == f.readline()
        for process in processes:
            assert not psutil.pid_exists(process.pid), f"{process} is still alive"
    @staticmethod
    def _procs_in_pgroup(pgid):
        for proc in psutil.process_iter(attrs=['pid', 'name']):
            try:
                if os.getpgid(proc.pid) == pgid and proc.pid != 0:
                    yield proc
            except OSError:
                pass