BIND 10 #2791: Try to work around the multi-CC hacks in XfrIn and CmdCtl with regards to rpc_call

[BIND 10 Development]

#2791: Try to work around the multi-CC hacks in XfrIn and CmdCtl with regards to
rpc_call
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                   Reporter:         |                 Owner:
  vorner                             |                Status:  new
                       Type:  task   |             Milestone:  New Tasks
                   Priority:         |              Keywords:
  medium                             |             Sensitive:  0
                  Component:         |           Sub-Project:  DNS
  Inter-module communication         |  Estimated Difficulty:  0
               CVSS Scoring:         |           Total Hours:  0
            Defect Severity:  N/A    |
Feature Depending on Ticket:         |
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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 The said modules have threads and have a inelegant hack because of them.
 They have one `ModuleCCSession` to listen for commands coming to them. But
 as this is blocking in one thread, the other threads use separate
 `CCSession` to send commands out (without any locking on it, which is
 dangerous, but a different issue).

 However, the `rpc_call` method that should be used instead of low-level
 JSON handling and `group_sendmsg` + `group_recvmsg` pair, is available on
 `ModuleCCSession` only, so it can't be used now.

 Try to work around this by creating a `ModuleCCSession` instead of the
 second `CCSession` with `None` as the command handlers, etc. Do not start
 it. It might or might not work, see if there are any strange side effects.
 If it works, replace the low-level calls with the `rpc_call` method.

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Ticket URL: <http://bind10.isc.org/ticket/2791>
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