Clean up executor interchange's log #511
Description
Executor interchange's log interchange.log file includes lines like
2021-06-10 16:20:39.153 interchange.strategy.simple:50 [INFO] Task breakdown [('interchange', 0, True), ('20d475621d87', 0, True)],
which is generated every second. We would like to clean then up, e.g., when there is no outstanding task, we can change the logging level to DEBUG.