RFR: CODETOOLS-7902907: jcstress: Change "FAILED" to "N/A" in probing code

[Aleksey Shipilev]

"FAILED" confuses users when received from the fairly innocuous code. "N/A" should work better.

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Commit messages:
 - CODETOOLS-7902907: jcstress: Change "FAILED" to "N/A" in probing code

Changes: https://git.openjdk.java.net/jcstress/pull/38/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=38&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902907
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/38.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/38/head:pull/38

PR: https://git.openjdk.java.net/jcstress/pull/38