LoggableCQLClient implementation

Implemented a class that takes CQLClient and log instance and logs and times every query getting
executed.
TODO: Write tests
@dreid recommended changes and tests added
not using log.bind - thanks @dreid

since it is specific to otter. Instead sticking with log.msg() only
hiding interal members
Merge pull request #25 from rackerlabs/logging

Logging CQLClient implementation