RFR: 8292880: Improve debuggee logging for com/sun/jdi/ClassUnloadEventTest.java

[Chris Plummer]

In order to help debug [JDK-8292879](https://bugs.openjdk.org/browse/JDK-8292879) failures, turn on class unload tracing in the debuggee and also have the debugger dump all the debuggee output. See the CR for example output.

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Commit messages:
 - Improve debuggee output.

Changes: https://git.openjdk.org/jdk/pull/10004/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10004&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292880
  Stats: 25 lines in 1 file changed: 22 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/10004.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10004/head:pull/10004

PR: https://git.openjdk.org/jdk/pull/10004