Remove compile time transport interface switch

- Remove the compile time check of the transport implementation.
  The transport (zeromq/nanomsg) can be chosen at run time with:
  `device.SetTransport("zeromq"); // possible values are "zeromq" and "nanomsg"`.

  For devices that use FairMQProgOptions, the transport can be configured via cmd option:
  `--transport zeromq` or `--transport nanomsg`. Default values is "zeromq".
  The device receives the configured value with:
  `device.SetTransport(config.GetValue<std::string>("transport"));`

  Old method of setting transport still works. But the NANOMSG constant is not defined.

- Remove old `fairmq/prototest` directory. It was only used as a test for protobuf.
  The protobuf part of Tutorial3 does the same (with different values).

- Fix a bug in FairMQPollerNN, where the `revents` value was not initialized.
  This caused the `poller->CheckOutput()` to trigger when it should not.

examples/MQ/8-multipart/runExample8Sink.cxx

@@ -19,12 +19,6 @@
 #include "FairMQProgOptions.h"
 #include "FairMQExample8Sink.h"
 
-#ifdef NANOMSG
-#include "FairMQTransportFactoryNN.h"
-#else
-#include "FairMQTransportFactoryZMQ.h"
-#endif
-
 int main(int argc, char** argv)
 {
     FairMQExample8Sink sink;
@@ -48,13 +42,7 @@ int main(int argc, char** argv)
 
         LOG(INFO) << "PID: " << getpid();
 
-#ifdef NANOMSG
-        FairMQTransportFactory* transportFactory = new FairMQTransportFactoryNN();
-#else
-        FairMQTransportFactory* transportFactory = new FairMQTransportFactoryZMQ();
-#endif
-
-        sink.SetTransport(transportFactory);
+        sink.SetTransport(config.GetValue<std::string>("transport"));
 
         sink.SetProperty(FairMQExample8Sink::Id, id);