Refactor the transport interface

- give transport Initialize() method with access to device config.
 - avoid using global context in the transport.
 - simplify shutdown procedure (no need for extra thread).

fairmq/FairMQChannel.h

@@ -258,7 +258,7 @@ class FairMQChannel
     bool CheckCompatibility(std::vector<std::unique_ptr<FairMQMessage>>& msgVec) const;
 
     void InitTransport(std::shared_ptr<FairMQTransportFactory> factory);
-    bool InitCommandInterface(int numIoThreads);
+    bool InitCommandInterface();
 
     bool HandleUnblock() const;