Detect commandeered revisions

[tomrittervg]

In Bug 1930832 a developer commandeered a phab revision (which is totally fine and encouraged) and later Updatebot tried to abandon it, which failed when it couldn't. The error it got back from phabricator was:

Got an error from phabricator when trying to abandon 228765: {'error': 'ERR-CONDUIT-CORE', 'errorMessage': 'ERR-CONDUIT-CORE: <differential.revision.edit> Validation errors:\n  - You can not abandon this revision because you are not the author. You can only abandon revisions you own. You can change this behavior by adjusting the "differential.always-allow-abandon" setting in Config.', 'response': None}

We could detect this error and handle it more gracefully.

[linabutler]

Thanks for filing this, @tomrittervg! Would it also be possible to not close the bug as a duplicate if the revision is commandeered? I think I've commandeered Updatebot's revisions once or twice before, but always landed them before there were new upstream changes—bug 1930832 is a bit of an odd one out.

[tomrittervg]

That makes sense to me!