BIND 10 #380: Remove duplicate code from _setup_session and config_handler

[BIND 10 Development]

#380: Remove duplicate code from _setup_session and config_handler
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      Reporter:  zzchen_pku         |        Owner:  zzchen_pku
          Type:  enhancement        |       Status:  reviewing 
      Priority:  major              |    Milestone:            
     Component:  secondary manager  |   Resolution:            
      Keywords:                     |    Sensitive:  0         
Estimatedhours:  0.0                |        Hours:  0         
      Billable:  1                  |   Totalhours:  0         
      Internal:  0                  |  
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Comment(by zzchen_pku):

 Replying to [comment:3 vorner]:
 > However, there's a small question this reminded me of (not direcly
 related to this change) ‒ from a user point of view, wouldn't it be better
 if whatever set the value said „0.6 is too much, I'm setting it to 0.5“
 instead of just silently setting it? I could imagine a user furiously
 trying to set his 0.6 and saying „Hey, why it ignores me?“. Do we want do
 to this kind of thing later on somewhere? Or, is the logic somewhere I
 didn't notice? Should I bring it to ML or is it already written somewhere?
 Good suggestion, I have updated the log message in r3297.
 You can find the jitter logic at
 [http://bind10.isc.org/wiki/SecondaryManager].

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Ticket URL: <https://bind10.isc.org/ticket/380#comment:4>
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