RFR: Use "out" field consistently in JCStress

[Johnny Lim]

This PR changes to use `out` field consistently in the `JCStress` as it would be better for internal consistency although it's effectively same as before.

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Commit messages:
 - Use "out" field consistently in JCStress

Changes: https://git.openjdk.org/jcstress/pull/151/files
  Webrev: https://webrevs.openjdk.org/?repo=jcstress&pr=151&range=00
  Stats: 5 lines in 1 file changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jcstress/pull/151.diff
  Fetch: git fetch https://git.openjdk.org/jcstress.git pull/151/head:pull/151

PR: https://git.openjdk.org/jcstress/pull/151