RFR: CODETOOLS-7903184: Update OS version check

[Jonathan Gibbons]

Please review a small fix to be slightly more permissive in the check for the os.version property, and allow a double-dotted number (like 1.2.3) to be accepted as better than a single-dotted prefix (like 1.2).

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Commit messages:
 - CODETOOLS-7903184: Update OS version check

Changes: https://git.openjdk.java.net/jtreg/pull/83/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=83&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903184
  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/83.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/83/head:pull/83

PR: https://git.openjdk.java.net/jtreg/pull/83