RFR: jcheck: make merge committers configurable

[Robin Westberg]

On Wed, 4 Mar 2020 15:05:04 GMT, Erik Helin <ehelin at openjdk.org> wrote:

> Hi all,
> 
> please review this patch that adds an additional configuration to the
> "committers" check. We now support setting usernames that are allowed to be
> committers of merge commits even though they are not part of the project. This
> is useful for allowing automated merge commits to pass jcheck.
> 
> Testing:
> - `make test` passes on Linux x64
> - Added two new unit tests
> 
> Thanks,
> Erik

Looks good as well!

-------------

Marked as reviewed by rwestberg (Reviewer).

PR: https://git.openjdk.java.net/skara/pull/494