RFR: 8373362: Http3TestServer should not log an exception stack trace when it is stopping normally

[Daniel Fuchs]

This a test fix only. The Http3TestServer has an additional level of logging that will print a full stack trace if an exception is thrown by the exchange handler. Printing the full stack trace is not helpful when the underlying server is stopping due to no error (typically when stop() is being called), and can clutter the log, making them more difficult to analyze.

This change turns off calling Throwable.printStackTrace() in such a case.

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Commit messages:
 - 8373362: Http3Server should not log an exception stack trace when it is stopping normally

Changes: https://git.openjdk.org/jdk/pull/28743/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28743&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373362
  Stats: 23 lines in 2 files changed: 22 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/28743.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28743/head:pull/28743

PR: https://git.openjdk.org/jdk/pull/28743