RFR: CODETOOLS-7902850: jcstress: Rework internal interfaces to get one TestResult per VM invocation

[Aleksey Shipilev]

Current jcstress code reports the TestResult for each iteration. While convenient to see the progress, it is ultimately noisy, and gets in the way of capturing the per-VM output. We can just accept a single test result per VM invocation, and rely on multiple forks to get verbose progress for long running tests.

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Commit messages:
 - CODETOOLS-7902850: jcstress: Rework internal interfaces to get one TestResult per VM invocation
 - Remove iterations

Changes: https://git.openjdk.java.net/jcstress/pull/12/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=12&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902850
  Stats: 57 lines in 7 files changed: 16 ins; 11 del; 30 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/12.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/12/head:pull/12

PR: https://git.openjdk.java.net/jcstress/pull/12