RFR: CODETOOLS-7903155: replace single use of `rsync` with `cp -R`

[Jonathan Gibbons]

Please review a simple test-only fix to replace the one single use of `rsync` with equivalent  `rm ...` `cp -R`

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Commit messages:
 - CODETOOLS-7903155: replace single use of `rsync` with `cp -R`

Changes: https://git.openjdk.java.net/jtreg/pull/73/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=73&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903155
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/73.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/73/head:pull/73

PR: https://git.openjdk.java.net/jtreg/pull/73