RFR: pr: hint about two reviewers for some labels

[Erik Helin]

Hi all,

please review this patch that makes it possible to configure per repository whether certain labels should cause a hint
in the integration message about two reviewers to be displayed.

Testing:
- [x] Added a new unit test
- [x] `make test` passes on Linux x64

Thanks,
Erik

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Commit messages:
 - pr: hint about two reviewers for some labels

Changes: https://git.openjdk.java.net/skara/pull/844/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=844&range=00
  Stats: 86 lines in 5 files changed: 81 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/skara/pull/844.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/844/head:pull/844

PR: https://git.openjdk.java.net/skara/pull/844