RFR: Add topological merge bot

[Jorn Vernee via github.com]

The pull request has been updated with additional changes.

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Added commits:
 - 4ffe0b07:	Do a hard rest after failed push.

Pull request:
https://git.openjdk.java.net/skara/pull/105

Webrevs:
 - full: https://webrevs.openjdk.java.net/skara/105/webrev.02
 - inc: https://webrevs.openjdk.java.net/skara/105/webrev.01-02

Updated full patch:
https://git.openjdk.java.net/skara/pull/105.diff

Fetch command:
git fetch https://git.openjdk.java.net/skara pull/105/head:pull/105