RFR: CODETOOLS-7903185: Update RerunTest for latest JUnit

[Jonathan Gibbons]

Please review a small test fix for RerunTest following the recent update for JUnit.
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Hamcrest (now typically part of the JUnit uber-jar) should not be expected/required to be on the test class path

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Commit messages:
 - CODETOOLS-7903185: Update RerunTest for latest JUnit

Changes: https://git.openjdk.java.net/jtreg/pull/84/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=84&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903185
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/84.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/84/head:pull/84

PR: https://git.openjdk.java.net/jtreg/pull/84