BIND 10 #1101: log message .py's should be installed under site-packages/isc/

[BIND 10 Development]

#1101: log message .py's should be installed under site-packages/isc/
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            Reporter:  jinmei        |                        Owner:
                Type:  defect        |                       Status:  new
            Priority:  major         |                    Milestone:  Next-
           Component:  logging       |  Sprint-Proposed
           Sensitive:  0             |                     Keywords:
         Sub-Project:  Core          |              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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 Currently, log messages in the form of python scripts (such as
 cfgmgr_messages.py) are installed in $(pyexec), which would be
 something like /usr/local/lib/python3.1/site-packages and is
 shared by other third-party python modules.

 As I commented in #764 (http://bind10.isc.org/ticket/764#comment:8),
 I don't think it a good practice.  To summarize the points:
 - to be in such a generic package directory, the file names are
   (generally) too generic, which would confuse users and might cause
   conflict with other modules.
 - It would also look awkward in the caller (such as xfrout.py)
   side: most of BIND 10 modules are imported with a prefix of "isc",
   but python modules for the log messages are missing it.

 I suggest making a separate directory under "isc", e.g,
 "isc/log_message" and install all *_messages.py files there.
 Note that we'd need something like what I did for #983 (commit
 b9bc51b): we'd need a separate variable in configure.ac, and
 specify the destination of the log files as
 $(PYTHON_SITEPKG_DIR)/isc/log_message

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Ticket URL: <https://bind10.isc.org/ticket/1101>
BIND 10 Development <http://bind10.isc.org>
BIND 10 Development