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.

fairmq/FairMQDevice.cxx

@@ -27,6 +27,11 @@
 #include "FairMQDevice.h"
 #include "FairMQLogger.h"
 
+#include "FairMQTransportFactoryZMQ.h"
+#ifdef NANOMSG_FOUND
+#include "FairMQTransportFactoryNN.h"
+#endif
+
 using namespace std;
 
 // boost::function and a wrapper to catch the signals
@@ -85,6 +90,12 @@ void FairMQDevice::SignalHandler(int signal)
 
 void FairMQDevice::InitWrapper()
 {
+    if (!fTransportFactory)
+    {
+        LOG(ERROR) << "Transport not initialized. Did you call SetTransport()?";
+        exit(EXIT_FAILURE);
+    }
+
     if (!fCmdSocket)
     {
         fCmdSocket = fTransportFactory->CreateSocket("pub", "device-commands", fNumIoThreads);
@@ -454,6 +465,32 @@ void FairMQDevice::SetTransport(FairMQTransportFactory* factory)
     fTransportFactory = factory;
 }
 
+void FairMQDevice::SetTransport(const string& transport)
+{
+    if (transport == "zeromq")
+    {
+        fTransportFactory = new FairMQTransportFactoryZMQ();
+    }
+#ifdef NANOMSG_FOUND
+    else if (transport == "nanomsg")
+    {
+        fTransportFactory = new FairMQTransportFactoryNN();
+    }
+#endif
+    else
+    {
+        LOG(ERROR) << "Unknown transport implementation requested: "
+                   << transport
+                   << ". Supported are "
+                   << "\"zeromq\""
+#ifdef NANOMSG_FOUND
+                   << ", \"nanomsg\""
+#endif
+                   << ". Exiting.";
+        exit(EXIT_FAILURE);
+    }
+}
+
 void FairMQDevice::LogSocketRates()
 {
     timestamp_t t0;