RFR: 7903813: Tag enablePreview with false should take precedence

[Christian Stein]

Please review this change to let tests with `enablePreview=false` take precedence over for example libraries that require preview features being enabled.

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Commit messages:
 - 7903813: Tag enablePreview with false should take precedence

Changes: https://git.openjdk.org/jtreg/pull/225/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=225&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903813
  Stats: 24 lines in 4 files changed: 14 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jtreg/pull/225.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/225/head:pull/225

PR: https://git.openjdk.org/jtreg/pull/225