[Buildbot] #2588: Check in upgrade_master that `rotateLength` and `maxRotatedFiles` are valid

[Buildbot trac]

#2588: Check in upgrade_master that `rotateLength` and `maxRotatedFiles` are valid
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Reporter:  rutsky     |       Owner:  Jc2k
    Type:  undecided  |      Status:  closed
Priority:  blocker    |   Milestone:  0.8.9
 Version:  0.8.8      |  Resolution:  fixed
Keywords:             |
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Comment (by Andriy Senkovych <jolly_roger@…>):

 In [changeset:"d217eda47027ad7407d9bc7afd6d14186fbc2994"]:
 {{{
 #!CommitTicketReference repository=""
 revision="d217eda47027ad7407d9bc7afd6d14186fbc2994"
 Add more information about buildbot upgrade errors (Refs: #2588)
 }}}

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Ticket URL: <http://trac.buildbot.net/ticket/2588#comment:4>
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