[Buildbot] #3433: p4client argument description is incorrect

[Buildbot trac]

#3433: p4client argument description is incorrect
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Reporter:  rutsky     |       Owner:  rutsky
    Type:  undecided  |      Status:  new
Priority:  minor      |   Milestone:  0.9.0
 Version:  master     |  Resolution:
Keywords:             |
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Comment (by dustin):

 The actual default is
 `Interpolate('buildbot_%(prop:slavename)s_%(prop:buildername)s')`

 Your fix looks good.

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Ticket URL: <http://trac.buildbot.net/ticket/3433#comment:3>
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