RFR: 8301644: com/sun/jdi/JdbStopThreadTest.java fails after JDK-8300811

[Chris Plummer]

This test started failing after [JDK-8300811](https://bugs.openjdk.org/browse/JDK-8300811), which made the jdb ThreadStartRequest and ThreadDeathRequest use SUSPEND_NONE instead of SUSPEND_ALL. This sped up the handling of these events a lot, which has impacted the timing of this test and exposed a bug.

The 2nd (last) breakpoint this test sets up uses SUSPEND_NONE. The debuggee quickly exits after hitting the breakpoint because it is not suspended. This puts the test at risk of having the debuggee exit before jdb can produce the full output for the breakpoint that includes the line number information. The test is looking for this output When it is not there, the test fails. Although the risk was always there, it was made worse by speeding up the handling of the ThreadDeath event. This is why this issue is also only seen on product builds (jdb needs to be running fast).

This failure is somewhat noisy so I'd like to push it quickly, but it should still have two reviews.

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Commit messages:
 - Fix JdbStopThreadTest.java after JDK-8301644 broke it.

Changes: https://git.openjdk.org/jdk/pull/12378/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12378&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301644
  Stats: 8 lines in 1 file changed: 6 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12378.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12378/head:pull/12378

PR: https://git.openjdk.org/jdk/pull/12378