RFR: 8310551: vmTestbase/nsk/jdb/interrupt/interrupt001/interrupt001.java timed out due to missing prompt

[Chris Plummer]

After [JDK-8308232](https://bugs.openjdk.org/browse/JDK-8308232), both the test and the debuggee shared the same waittime of 5 minutes. The test would wait up to 5 minutes for the expected prompt, but the debuggee would also in some cases wait 5 minutes before generating the prompt, which sometimes was just a bit too late. Before [JDK-8308232](https://bugs.openjdk.org/browse/JDK-8308232), the debuggee would wait at most 2 minutes before generating the prompt, so it was always generated in time.

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Commit messages:
 - Improve comment.
 - Alternate fix. Don't call wait() if all threads have been interrupted.
 - Use 200ms delay rather than rely on "waittime", which is usually 5 minutes.

Changes: https://git.openjdk.org/jdk/pull/14817/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14817&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310551
  Stats: 9 lines in 2 files changed: 5 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/14817.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14817/head:pull/14817

PR: https://git.openjdk.org/jdk/pull/14817