Clean up logging.

Some information became redundant since we started using MDC.
Merge pull request #79 from m1ch1/logging

Clean up logging.
netty transport cleanup.

- Remove unused close() method.
- Don't clear the senders map from the shutdown method. Instead, let
  the ErrorHandler do the clean up.
- Don't print stack trace for connection failed error.
- Add a comment and some asserts around handling disconnect.
Merge pull request #81 from m1ch1/netty

netty transport cleanup.