RFR: 8293000: Review running times of jshell regression tests

[Adam Sotona]

Some of the jshell tests have been identified as long-running.

This patch reduces tests runtimes with multiple tricks:

- local execution control is used in heavily parametrized and fragmented tests to eliminate JVM startups
- some tests have been defragmented
- unnecessary Thread::stop has been removed

Measured test run times before and after application of this patch:
- ClassMembersTest 23.964ms ->  9.195ms
- ToolBasicTest 24.281ms -> 14.955ms
- FailOverExecutionControlHangingListenTest 31.221ms -> 5.780ms
- FailOverExecutionControlDyingLaunchTest 31.221ms -> 6.050ms
- FailOverExecutionControlHangingLaunchTest 31.303ms -> 5.832ms
- CompletionSuggestionTest 10.523ms -> 4.940ms
- SimpleRegressionTest 3.629ms -> 1.304ms

Please review the test changes.

Thanks,
Adam

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Commit messages:
 - 8293000: Review running times of jshell regression tests

Changes: https://git.openjdk.org/jdk/pull/10428/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10428&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293000
  Stats: 42 lines in 5 files changed: 23 ins; 10 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/10428.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10428/head:pull/10428

PR: https://git.openjdk.org/jdk/pull/10428