BIND 10 #1457: use the difference normalizer in the DDNS module

[BIND 10 Development]

#1457: use the difference normalizer in the DDNS module
-------------------------------------+-------------------------------------
                   Reporter:  jelte  |                 Owner:  vorner
                       Type:  task   |                Status:  reviewing
                   Priority:         |             Milestone:
  medium                             |  Sprint-20120612
                  Component:  DDNS   |            Resolution:
                   Keywords:         |             Sensitive:  0
            Defect Severity:  N/A    |           Sub-Project:  DNS
Feature Depending on Ticket:  DDNS   |  Estimated Difficulty:  3
        Add Hours to Ticket:  0      |           Total Hours:  22
                  Internal?:  0      |
-------------------------------------+-------------------------------------

Comment (by jinmei):

 Note: we need to create an updater before the prerequisite check
 and use its finder (updater.find()), instead of `UpdateSession.__finder`.

-- 
Ticket URL: <http://bind10.isc.org/ticket/1457#comment:16>
BIND 10 Development <http://bind10.isc.org>
BIND 10 Development