RFR: 7904052: Allow JCov tests to be run by JTReg

[Alexandre Iline]

JCov provides better isolation and better control over the execution environment.
For now I kept the testng test subject, up for discussion.

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Commit messages:
 - And the target to run tests
 - CODETOOLS-7904052: Allow JCov tests to be run by JTReg

Changes: https://git.openjdk.org/jcov/pull/63/files
  Webrev: https://webrevs.openjdk.org/?repo=jcov&pr=63&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7904052
  Stats: 13 lines in 2 files changed: 13 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jcov/pull/63.diff
  Fetch: git fetch https://git.openjdk.org/jcov.git pull/63/head:pull/63

PR: https://git.openjdk.org/jcov/pull/63