[Buildbot] #3572: Restore logHorizon and buildHorizon functionality

[Buildbot trac]

#3572: Restore logHorizon and buildHorizon functionality
------------------------+-------------------
Reporter:  tardyp       |      Owner:
    Type:  enhancement  |     Status:  new
Priority:  major        |  Milestone:  0.9.1
 Version:  master       |   Keywords:
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 Its important to have logHorizon functionality to allow users to easily
 cleanup old builds and control the overgrowth of their database.

 This could be implemented easily as a separate service:

 {{{
 c['services'].append(HouseKeepingService(logHorizon="1w",
 buildHorizon="1m"))
 }}}

 with appropriate legacy API translation.

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Ticket URL: <http://trac.buildbot.net/ticket/3572>
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