RFR: 8313612: Use JUnit in lib-test/jdk tests

[Qing Xiao]

Modified all tests under lib-test/jdk to use JUnit

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Commit messages:
 - Corrected the testSecondArrayIsNull() in ArrayDiffTest and modified format.
 - Modified all tests under lib-test/jdk to use JUnit

Changes: https://git.openjdk.org/jdk/pull/15131/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15131&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313612
  Stats: 288 lines in 5 files changed: 45 ins; 26 del; 217 mod
  Patch: https://git.openjdk.org/jdk/pull/15131.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15131/head:pull/15131

PR: https://git.openjdk.org/jdk/pull/15131