BIND 10 #1889: bind10 --config-file does not work

[BIND 10 Development]

#1889: bind10 --config-file does not work
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                   Reporter:  jreed  |                 Owner:  UnAssigned
                       Type:         |                Status:  reviewing
  defect                             |             Milestone:
                   Priority:         |  Sprint-20120515
  medium                             |            Resolution:
                  Component:  Boss   |             Sensitive:  0
  of BIND                            |           Sub-Project:  Core
                   Keywords:         |  Estimated Difficulty:  5
            Defect Severity:  N/A    |           Total Hours:  0
Feature Depending on Ticket:         |
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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Changes (by jelte):

 * owner:  jelte => UnAssigned
 * status:  assigned => reviewing


Comment:

 Ready for review, added a helper function for determining the correct path
 and file (there are a few options, described in the docstring), separate
 function also makes it much easier to test :)

 I also added a log info message that prints which file in ends up using

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Ticket URL: <http://bind10.isc.org/ticket/1889#comment:6>
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