RFR: 397: Extend the additional errors section with hidden jcheck entries

[Robin Westberg]

Hi all,

Please review this change that displays jcheck failure messages that are "hidden" (not shown as an item in the progress
list) in the PR body error section.

Best regards,
Robin

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Commit messages:
 - Display non-progress-list jcheck failures in the PR status body

Changes: https://git.openjdk.java.net/skara/pull/620/files
 Webrev: https://webrevs.openjdk.java.net/skara/620/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-397
  Stats: 119 lines in 5 files changed: 85 ins; 12 del; 22 mod
  Patch: https://git.openjdk.java.net/skara/pull/620.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/620/head:pull/620

PR: https://git.openjdk.java.net/skara/pull/620