BIND 10 #2149: retry send 'setup connection' in b10-ddns

[BIND 10 Development]

#2149: retry send 'setup connection' in b10-ddns
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            Reporter:  jelte         |                        Owner:
                Type:  defect        |                       Status:  new
            Priority:  medium        |                    Milestone:  New
           Component:  Unclassified  |  Tasks
           Sensitive:  0             |                     Keywords:
         Sub-Project:  DNS           |              Defect Severity:  N/A
Estimated Difficulty:  0             |  Feature Depending on Ticket:
         Total Hours:  0             |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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 ticket 1986 added a command that is sent from b10-ddns to b10-auth, which
 sets up the internal connection to forward packets.

 It also contains a message from auth to ddns should auth be restarted.
 However, on startup, if ddns is just slightly faster than auth in getting
 started, auth never gets the message, and b10-ddns hangs for 4 seconds
 waiting for an answer (the connection does get set up eventually, but it
 will cause errors if it is attempted to be used initially, b10-ddns is
 dead in the water for the full 4 second, not answering to commands and
 updates).

 Fundamentally, the problem is the lack of real async io in b10-ddns,
 however, a quick workaround would be to set the internal timeout lower
 than the default, and retry a few times before erroring.

 We also need an option for the 'nonblocking' version of check_command to
 check for multiple commands I think.

 (I have some code, which i'll put in the branch, but it may need some unit
 tests, and now my lettuce tests fail on an entirely different cmdctl
 error)

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Ticket URL: <http://bind10.isc.org/ticket/2149>
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