[Buildbot] #2956: Provide latent Docker build slave

[Buildbot trac]

#2956: Provide latent Docker build slave
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Reporter:  sa2ajj                 |       Owner:  Ben
    Type:  enhancement            |      Status:  assigned
Priority:  patches-accepted       |   Milestone:  0.9.+
 Version:  master                 |  Resolution:
Keywords:  docker, slave, latent  |
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Comment (by sa2ajj):

 And, by the way, this modification can go to master: `buildslave create-
 slave` can put the provided values so that they are used as defaults,
 while the abovementioned environment variables would override these
 defaults.

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Ticket URL: <http://trac.buildbot.net/ticket/2956#comment:11>
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