RFR: Show a summary of pre-submit testing results in the PR body (if any)

[Robin Westberg]

Now that we are executing pre-submit tests for certain OpenJDK repositories, we can also display a summary of the
results in the PR body, to help reviewers determine the test status of a change.

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Commit messages:
 - Initial implementation

Changes: https://git.openjdk.java.net/skara/pull/855/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=855&range=00
  Stats: 202 lines in 11 files changed: 196 ins; 1 del; 5 mod
  Patch: https://git.openjdk.java.net/skara/pull/855.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/855/head:pull/855

PR: https://git.openjdk.java.net/skara/pull/855