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
LOGGING_CONFIG = {
    'version': 1,
    'disable_existing_loggers': False,
    'formatters': {
        'airflow.task': {'format': '[%(asctime)s] {{%(filename)s:%(lineno)d}} %(levelname)s - %(message)s'},
    },
    'handlers': {
        'console': {
            'class': 'logging.StreamHandler',
            'formatter': 'airflow.task',
            'stream': 'ext://sys.stdout',
        }
    },
    'loggers': {'airflow': {'handlers': ['console'], 'level': 'INFO', 'propagate': False}},
}
class TestStandardTaskRunner(unittest.TestCase):
    @classmethod
    def setUpClass(cls):
        dictConfig(LOGGING_CONFIG)
    @classmethod
    def tearDownClass(cls):
        airflow_logger = logging.getLogger('airflow')
        airflow_logger.handlers = []
        airflow_logger.propagate = True
        try:
            clear_db_runs()
        except Exception:  
            
            pass
    def test_start_and_terminate(self):