[Buildbot] #3244: Add slack status target

[Buildbot trac]

#3244: Add slack status target
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Reporter:  dank              |      Owner:
    Type:  enhancement       |     Status:  new
Priority:  patches-accepted  |  Milestone:
 Version:  0.8.10            |   Keywords:
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 The cool kids are giving up on email and moving everything to slack,
 which mystifies me, but you have to keep the users happy.
 So buildbot could use a slack status target for pushing errors
 to where the authors of the broken code hang out.

 Several exist, see e.g.
 https://github.com/mindmatters/buildbot-status-slack
 https://github.com/rickmak/buildbot-slack
 but it'd be nice if one were bundled.

 Note:
 http://git.ganeti.org/buildbot.git/ is unrelated... that slack
 is not the slack you're looking for.

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Ticket URL: <http://trac.buildbot.net/ticket/3244>
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Buildbot: build/test automation