RFR: CODETOOLS-7903040: jcstress: Introduce stress configuration multipliers

[Aleksey Shipilev]

Stress C2 modes are random, it makes sense to run them in more forks to have more opportunities for (un)lucky compilation.

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Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/jcstress/pull/99/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=99&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903040
  Stats: 42 lines in 3 files changed: 21 ins; 3 del; 18 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/99.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/99/head:pull/99

PR: https://git.openjdk.java.net/jcstress/pull/99