[Buildbot] #3069: make it possible for service specific admins to use jexec

[Buildbot trac]

#3069: make it possible for service specific admins to use jexec
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Reporter:  sa2ajj  |      Owner:
    Type:  task    |     Status:  new
Priority:  major   |  Milestone:  sys - on-bb-infra
 Version:          |   Keywords:  ansible
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 From #3004:

 > `jexec <appropriate jail> sh` for non-admins with access to a single
 jail

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Ticket URL: <http://trac.buildbot.net/ticket/3069>
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Buildbot: build/test automation