RFR: CODETOOLS-7903221: broken self-tests

[Jonathan Gibbons]

Please review a couple of test changes to make them more robust in the face of using alternate locations for the build directory, and choice of JUnit library

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Commit messages:
 - Merge remote-tracking branch 'upstream/master' into jtreg.7113596.broken-tests
 - CODETOOLS-7903221: broken self-tests

Changes: https://git.openjdk.org/jtreg/pull/90/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=90&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903221
  Stats: 7 lines in 2 files changed: 4 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jtreg/pull/90.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/90/head:pull/90

PR: https://git.openjdk.org/jtreg/pull/90