refactor to more idiomatic RAII

* FairMQTransportFactoryZMQ: move the config invariant
    initialization to ctor
  * FairMQChannel: add new ctor that creates usable channel
  * FairMQSocket*: close sockets in dtor
  * FairMQTransportFactory*: terminate context in dtor
  * FairMQChannel: add Bind/Connect facades (for explicit control, e.g. timing)

fairmq/zeromq/FairMQSocketZMQ.cxx

@@ -565,4 +565,5 @@ int FairMQSocketZMQ::GetConstant(const string& constant)
 
 FairMQSocketZMQ::~FairMQSocketZMQ()
 {
+    Close();
 }

fairmq/zeromq/FairMQTransportFactoryZMQ.cxx

@@ -33,6 +33,11 @@ FairMQTransportFactoryZMQ::FairMQTransportFactoryZMQ()
         LOG(ERROR) << "failed creating context, reason: " << zmq_strerror(errno);
         exit(EXIT_FAILURE);
     }
+
+    if (zmq_ctx_set(fContext, ZMQ_MAX_SOCKETS, 10000) != 0)
+    {
+        LOG(ERROR) << "failed configuring context, reason: " << zmq_strerror(errno);
+    }
 }
 
 void FairMQTransportFactoryZMQ::Initialize(const FairMQProgOptions* config)
@@ -51,12 +56,6 @@ void FairMQTransportFactoryZMQ::Initialize(const FairMQProgOptions* config)
     {
         LOG(ERROR) << "failed configuring context, reason: " << zmq_strerror(errno);
     }
-
-    // Set the maximum number of allowed sockets on the context.
-    if (zmq_ctx_set(fContext, ZMQ_MAX_SOCKETS, 10000) != 0)
-    {
-        LOG(ERROR) << "failed configuring context, reason: " << zmq_strerror(errno);
-    }
 }
 
 FairMQMessagePtr FairMQTransportFactoryZMQ::CreateMessage() const
@@ -130,3 +129,8 @@ void FairMQTransportFactoryZMQ::Terminate()
         LOG(ERROR) << "shmem: Terminate(): context now available for shutdown";
     }
 }
+
+FairMQTransportFactoryZMQ::~FairMQTransportFactoryZMQ()
+{
+    Terminate();
+}

fairmq/zeromq/FairMQTransportFactoryZMQ.h

@@ -27,6 +27,7 @@ class FairMQTransportFactoryZMQ : public FairMQTransportFactory
 {
   public:
     FairMQTransportFactoryZMQ();
+    ~FairMQTransportFactoryZMQ() override;
 
     void Initialize(const FairMQProgOptions* config) override;
 
@@ -45,8 +46,6 @@ class FairMQTransportFactoryZMQ : public FairMQTransportFactory
     void Shutdown() override;
     void Terminate() override;
 
-    ~FairMQTransportFactoryZMQ() override {};
-
   private:
     static FairMQ::Transport fTransportType;
     void* fContext;