BIND 10 #2018: Use updater's finder in DDNS

[BIND 10 Development]

#2018: Use updater's finder in DDNS
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            Reporter:  jelte         |                        Owner:
                Type:  defect        |                       Status:  new
            Priority:  medium        |                    Milestone:  New
           Component:  Unclassified  |  Tasks
           Sensitive:  0             |                     Keywords:
         Sub-Project:  DNS           |              Defect Severity:  N/A
Estimated Difficulty:  0             |  Feature Depending on Ticket:
         Total Hours:  0             |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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 Currently the DDNS (if/when #1457 is merged) will create a separate Finder
 and Updater (through the Diff class), while it should really create the
 Diff and its updater, and use the updater's find methods.

 This needs a change to Diff, either it needs to be given an Updater, or it
 needs to be able to return its Updater. In the latter case, we'll also
 need to create the Diff, and its Updater during __get_update_zone, and set
 it to a private member as well.

 The latter approach is more work in terms of code, but probably pretty
 straightforward, and (i think) cleaner.

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Ticket URL: <http://bind10.isc.org/ticket/2018>
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