RFR: 2300: Do not list non-OpenJDK reviewers in Reviewers list

[Zhao Song]

This PR is trying to make skara bot list non-recognized user in a separate section in the PR body.

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Commit messages:
 - SKARA-2300

Changes: https://git.openjdk.org/skara/pull/1693/files
  Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1693&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2300
  Stats: 22 lines in 2 files changed: 19 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/skara/pull/1693.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1693/head:pull/1693

PR: https://git.openjdk.org/skara/pull/1693