RFR: CODETOOLS-7902908: jcstress: Rework footprint sanity checking code

[Aleksey Shipilev]

Current sanity checking code has a few problems: first, it executes actors without an executor, which violates the basic contract that every actor would run in the separate thread. Then, it also does more iterations than in should when min/max stride is 1.

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Commit messages:
 - CODETOOLS-7902908: jcstress: Rework footprint sanity checking code

Changes: https://git.openjdk.java.net/jcstress/pull/39/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=39&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902908
  Stats: 106 lines in 3 files changed: 58 ins; 18 del; 30 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/39.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/39/head:pull/39

PR: https://git.openjdk.java.net/jcstress/pull/39