BIND 10 #2203: separate CC Session from auth DataSourceConfigurator

[BIND 10 Development]

#2203: separate CC Session from auth DataSourceConfigurator
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            Reporter:  jinmei        |                        Owner:
                Type:  task          |                       Status:  new
            Priority:  medium        |                    Milestone:  Next-
           Component:  b10-auth      |  Sprint-Proposed
           Sensitive:  0             |                     Keywords:
         Sub-Project:  DNS           |              Defect Severity:  N/A
Estimated Difficulty:  0             |  Feature Depending on Ticket:
         Total Hours:  0             |  background zone loading
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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 A subtask of #2201.

 Not directly related to the feature goal, but (I believe) this
 refactor will help later development.

 What to do: instead of passing `Session` to the configurator ('s init()),
 define a separate command handler somewhere in auth, and do
 addRemoteConfig() with it.  The command handler will call
 `DataSourceConfigurator::reconfigure()`.

 also consider whether we can avoid using the configurator class as
 a singleton (i.e. a static object).  singleton is often the source
 of evils and often makes test harder due to its static nature.

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Ticket URL: <http://bind10.isc.org/ticket/2203>
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