RFR: CODETOOLS-7902880: jcstress: Improve test line reporting again

[Aleksey Shipilev]

Unfortunately, CODETOOLS-7902873 was not complete. The logic to ignore first test results does not account for the fact that many tests start at parallel, which means the initial flurry of the test results overestimates the sample rate hard. We can do a bit better.

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Commit messages:
 - Reconcile the reports again

Changes: https://git.openjdk.java.net/jcstress/pull/27/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=27&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902880
  Stats: 16 lines in 1 file changed: 2 ins; 7 del; 7 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/27.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/27/head:pull/27

PR: https://git.openjdk.java.net/jcstress/pull/27