Optimizing `rebuild` for the label-trigger scenario?

[icecrime]

The rebuild operation currently supports a single trigger label. If you want to configure multiple label to configuration associations, you need to repeat yourself in the configuration:

- repositories:     [ "docker/docker" ]
  triggers:
      pull_request: [ labeled ]
  operations:
      - type:       rebuild
        settings: {
            configurations: [ arm ],
            label:          "rebuild/arm",
        }
      - type:       rebuild
        settings: {
            configurations: [ experimental ],
            label:          "rebuild/experimental",
        }

Question: is that a good approach, or should rebuild made aware of a label to configuration mapping?

[icecrime]

Also, this would prevent the following torrent of logs:

time="2016-11-08T16:33:03-05:00" level=debug msg="received GitHub event" action=labeled event="pull_request" number=27745 repository="docker/docker" 
time="2016-11-08T16:33:03-05:00" level=info msg="running operation" operation=rebuild repository="docker/docker" 
time="2016-11-08T16:33:04-05:00" level=debug msg="rejecting pull request without label \"rebuild/arm\"" 
time="2016-11-08T16:33:04-05:00" level=info msg="running operation" operation=rebuild repository="docker/docker" 
time="2016-11-08T16:33:04-05:00" level=debug msg="rejecting pull request without label \"rebuild/experimental\"" 
time="2016-11-08T16:33:04-05:00" level=info msg="running operation" operation=rebuild repository="docker/docker" 
time="2016-11-08T16:33:04-05:00" level=debug msg="rejecting pull request without label \"rebuild/janky\"" 
time="2016-11-08T16:33:04-05:00" level=info msg="running operation" operation=rebuild repository="docker/docker" 
time="2016-11-08T16:33:04-05:00" level=debug msg="rejecting pull request without label \"rebuild/userns\"" 
time="2016-11-08T16:33:04-05:00" level=info msg="running operation" operation=rebuild repository="docker/docker" 
time="2016-11-08T16:33:04-05:00" level=debug msg="rejecting pull request without label \"rebuild/vendor\"" 
time="2016-11-08T16:33:04-05:00" level=info msg="running operation" operation=rebuild repository="docker/docker" 
time="2016-11-08T16:33:04-05:00" level=debug msg="rejecting pull request without label \"rebuild/win2lin\"" 
time="2016-11-08T16:33:04-05:00" level=info msg="running operation" operation=rebuild repository="docker/docker" 
time="2016-11-08T16:33:04-05:00" level=debug msg="rejecting pull request without label \"rebuild/windowsRS1\""