[Buildbot] #3645: consider using devpi-server in BB infrastructure

[Buildbot trac]

#3645: consider using devpi-server in BB infrastructure
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Reporter:  sa2ajj            |      Owner:
    Type:  task              |     Status:  new
Priority:  patches-accepted  |  Milestone:  sys - on-bb-infra
 Version:                    |   Keywords:
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 [http://doc.devpi.net/latest/ devpi-server] supports several scenarios
 useful for us:

 * fast PyPI mirror
 * uploading, testing and staging with private indexes (for testing
 packages before publishing on PyPI)

 alternatively we can just put something like
 [http://www.dctrwatson.com/2013/06/simple-pypi-caching-proxy/ simple nginx
 based proxy]

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Ticket URL: <http://trac.buildbot.net/ticket/3645>
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