replace custom logging with python standard library

This patch removes hdist_logging.py with the Python logging module. The logging configuration is in a yaml file, pretty standard.

* I left the "hit logpipe" command in there, though I still don't understand what its for. Is part of the unit test fixtures? I can take it out and hashdist works fine. See also https://groups.google.com/d/msg/hashdist/TApv422EmZA/LHCApTw8yC8J

* Python best practice is to not pass the logger around but use logging.getLogger() to access the singleton loggers. Replacing this would be the next step, but its not done here.