RFR: 8304065: HttpServer.stop should terminate immediately if no exchanges are in progress

[Mikhail Yankelevich]

HttpServer::stop will terminate the server immidiately after all exhcnages are complete.
If the exchanges take longer then the specified delay it will terminate straight after the delay, the same as the previous behaviour.

Used to wait until the delay is complete at all times, regardless of the number of active exchanges.

Tests based on @eirbjo work, so adding Erik as a contributor.

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Commit messages:
 - new line in the end of the test
 - JDK-8304065: HttpServer.stop should terminate immediately if no exchanges are in progress

Changes: https://git.openjdk.org/jdk/pull/25333/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25333&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304065
  Stats: 365 lines in 3 files changed: 350 ins; 0 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/25333.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25333/head:pull/25333

PR: https://git.openjdk.org/jdk/pull/25333