RFR: CODETOOLS-7902958: jcstress: Make sure tests have copyright headers

[Aleksey Shipilev]

Current license plugin ignores src/test/main, so many tests are missing copyright headers.

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Commit messages:
 - Correct copyright for tests
 - Make sure tests are copyrighted

Changes: https://git.openjdk.java.net/jcstress/pull/64/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=64&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902958
  Stats: 493 lines in 35 files changed: 422 ins; 9 del; 62 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/64.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/64/head:pull/64

PR: https://git.openjdk.java.net/jcstress/pull/64