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:  new       
  Priority:  major              |        Milestone:            
 Component:  secondary manager  |         Keywords:            
 Sensitive:  0                  |   Estimatedhours:  0         
     Hours:  0                  |         Billable:  1         
Totalhours:  0                  |         Internal:  0         
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 _setup_session and config_handler in zonemgr.py duplicate some code, need
 to remove them.

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Ticket URL: <https://bind10.isc.org/ticket/380>
BIND 10 Development <http://bind10.isc.org>
BIND 10 Development