RFR: CODETOOLS-7902904: jcstress: Explicit waits for VM shutdowns

[Aleksey Shipilev]

Current TestExecutor code spins in the 100ms-wait loop for re-starting the next epoch of scheduling. This is way too large a wait for -m sanity. Reducing it to 10ms throws the non-sanity runs under the bus. We should instead do explicit waits for VM shutdown, and restart the scheduling then.

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Commit messages:
 - CODETOOLS-7902904: jcstress: Explicit waits for VM shutdowns

Changes: https://git.openjdk.java.net/jcstress/pull/35/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=35&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902904
  Stats: 64 lines in 5 files changed: 47 ins; 10 del; 7 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/35.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/35/head:pull/35

PR: https://git.openjdk.java.net/jcstress/pull/35