[MINOR] maybe a log bug of PinotAdministrator

When using `pinot-admin.sh CreateSegment` if `overwrite` option is not specified but the output dir existed, it did not have any related prompt on console.
It should [log error in code](https://github.com/apache/incubator-pinot/blob/master/pinot-tools/src/main/java/org/apache/pinot/tools/admin/PinotAdministrator.java#L111), but looks print nothing. When using `Logger` instead of `AsyncLogger` will be ok.
A way to fix it is adding `LogManager.shutdown()` in main or try-catch-finally, is it a proper way?
Thanks

Start at pinot-tools/src/main/java/org/apache/pinot/tools/admin/PinotAdministrator.java around line 111 and reproduce the pinot-admin.sh CreateSegment case with an existing output directory and no overwrite option. Compare the Logger and AsyncLogger behavior mentioned in the issue, then verify that the error is visible before the command exits. No test file is mentioned in the issue.

Written by the indexing model from the issue text.