RFR: Move testing information from the PR body to checks

[Robin Westberg]

When summarizing pre-submit test results for a PR, show the results as a number of checks instead of a table in the PR body. This makes them more similar to the source information, and avoids excessive PR body updates.

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Commit messages:
 - Initial implementation

Changes: https://git.openjdk.java.net/skara/pull/962/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=962&range=00
  Stats: 1098 lines in 14 files changed: 626 ins; 467 del; 5 mod
  Patch: https://git.openjdk.java.net/skara/pull/962.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/962/head:pull/962

PR: https://git.openjdk.java.net/skara/pull/962