BIND 10 #3156: Create separate base-classes for the Finite State Machine logic in NameChangeTransaction class

[BIND 10 Development]

#3156: Create separate base-classes for the Finite State Machine logic in
NameChangeTransaction class
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            Reporter:  tmark         |                        Owner:  tmark
                Type:  enhancement   |                       Status:
            Priority:  low           |  accepted
           Component:  dhcp-ddns     |                    Milestone:  DHCP
            Keywords:                |  Outstanding Tasks
           Sensitive:  0             |                   Resolution:
         Sub-Project:  DHCP          |                 CVSS Scoring:
Estimated Difficulty:  0             |              Defect Severity:  N/A
         Total Hours:  0             |  Feature Depending on Ticket:
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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Comment (by tmark):

 I have created a new abstract class, d2/StateModel and then refactored
 !NameChangeTransaction to derive from it.  The general concept is the
 same, it is simply in its own class.  There were some minor improvements
 along the way.   The results are cleaner all the way around.

 Not sure if this needs a change log entry, but if so then I think this
 should suffice:
 {{{
 6xx.    [func]  tmark

 b10-dhcp-ddns Finite state machine logic was refactored into its own
 class,
 StateModel.
 (Trac# 3156,  git TBD)
 }}}

 Attached is a class diagram showing the new class:

 [[Image(state_model_nc_trans_classes.svg)]]

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Ticket URL: <http://bind10.isc.org/ticket/3156#comment:3>
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