Clean up log messages

This is just a general sweep of the log messages to update them
so they're all consistent.  The general changes are:

* Use log args instead of performing string interpolation of the
  message (``.debug('foo: %s', 'bar') not .debug('foo: %s' % bar))
* Remove log messages that log the name of the method.  This can
  be done via the log formatter if a dev needs this info.
* Add more context to log messages, this makes it easier to read the
  debug logs.
* Made sure the module level loggers were all called ``logger``, for
  consistency (retryhandler was the only one with a logger called
  ``log``).
* Try to keep the log format to be: "Capitalized full sentence."
  where appropriate.