Get rid of NetconfMessageFactory

This removes the use of deprecated ProtocolMessageFactory and
ProtocolHandlerFactory. Just instantiate appropriate Netty handlers
instead.

Change-Id: I98b6424af0256483be21c92dfdbe4c0ddbac7a9d
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "Get rid of NetconfMessageFactory"