RFR: 7903493: jcstress: Cut down test configurations

[Aleksey Shipilev]

Current full jcstress run takes about 60+ days on 36-core machine. This is driven by too many test configurations tested in the default config. We can cut down the test times (again) by re-examining the default run options.

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Commit messages:
 - First cut

Changes: https://git.openjdk.org/jcstress/pull/142/files
 Webrev: https://webrevs.openjdk.org/?repo=jcstress&pr=142&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903493
  Stats: 10 lines in 2 files changed: 1 ins; 7 del; 2 mod
  Patch: https://git.openjdk.org/jcstress/pull/142.diff
  Fetch: git fetch https://git.openjdk.org/jcstress.git pull/142/head:pull/142

PR: https://git.openjdk.org/jcstress/pull/142