RFR: Add testReport task to create a combined report

[Robin Westberg]

Hi all,

Please review this change that adds a new gradle task `testReport` that runs all tests (continuing even if there are
failures) and creates a combined report afterwards.

Best regards,
Robin

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Commit messages:
 - Add testReport task to create a combined report

Changes: https://git.openjdk.java.net/skara/pull/569/files
 Webrev: https://webrevs.openjdk.java.net/skara/569/webrev.00
  Stats: 24 lines in 1 file changed: 24 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/skara/pull/569.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/569/head:pull/569

PR: https://git.openjdk.java.net/skara/pull/569