tls: add isServer() method to TlsSession

This method returns a bool indicating if the TlsSession was
created as Server (true) or as Client (false).

Change-Id: I14f1c50d584430fc959134512ce11edaf029c198
Tuleap: #660

src/security/tls_session.h

@@ -138,6 +138,8 @@ public:
     // Returns the TLS session type ('server' or 'client')
     const char* typeName() const;
 
+    bool isServer() const { return isServer_; }
+
     // Request TLS thread to stop and quit. IO are not possible after that.
     void shutdown();