FYI: merge-bot: provide default values in conf

[Erik Helin]

Hi all,

please review this small patch that makes `MergeBotFactory` provide default
values for specification fields in the configures.

Testing:
- `make test` passes on Linux x64

Thanks,
Erik

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Commit messages:
 - merge-bot: provide default values in conf

Changes: https://git.openjdk.java.net/skara/pull/606/files
 Webrev: https://webrevs.openjdk.java.net/skara/606/webrev.00
  Stats: 12 lines in 3 files changed: 9 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/skara/pull/606.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/606/head:pull/606

PR: https://git.openjdk.java.net/skara/pull/606