BIND 10 #2213: revise LoadZoneCommand::exec() of b10-auth to use the configurator thread

[BIND 10 Development]

#2213: revise LoadZoneCommand::exec() of b10-auth to use the configurator thread
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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, depends on #2205, #2212

 This task revise the exec() method so it now just creates a "reload
 zone" command for the thread, and wakes up the thread with it.

 At this point, we can (should) deprecate
 `ConfigurableClientList::reload()`.

 When this task completes, zone reloading should now be possible
 without disrupting service.

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Ticket URL: <http://bind10.isc.org/ticket/2213>
BIND 10 Development <http://bind10.isc.org>
BIND 10 Development