Replace AppendableByteArrayInputStream in DirectDruidClient
* Replace with SequenceInputStream fueled by an enumeration of ChannelBufferInputStream which directly wrap the response context ChannelBuffer
* Added zero-length byte array when DirectDruidClient is done. This prevents an odd race condition on `done`.
Merge pull request #932 from metamx/directDruidClientSpeedupRebase

Replace AppendableByteArrayInputStream in DirectDruidClient