BIND 10 #2210: support "reconfigure" command in the configurator thread

[BIND 10 Development]

#2210: support "reconfigure" command in 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, depend on #2202, #2204, #2205.

 This task extends the newly introduced "data source configurator"
 thread in #2205 to support full data source reconfiguration in
 background (allowing the main thread to keep using the old
 configuration until new config is fully loaded).

 It does the following:
 - call `DataSourceConfiguratorGeneric::reconfigure()` (revised in #2204)
 - acquire the lock (introduced in #2202)
 - call `AuthSrv::setDataSourceClientLists()` (introduced in #2204) with
   the reconfigure() result
 - release the lock
 - let the returned old map from setDataSourceClientLists() be
   destroyed.

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Ticket URL: <http://bind10.isc.org/ticket/2210>
BIND 10 Development <http://bind10.isc.org>
BIND 10 Development