add handling for tcp handshake (#788)

Author: thelonelyvulpes

Neo4j.Driver/Neo4j.Driver/Internal/Connector/TcpSocketClient.cs

@@ -63,7 +63,7 @@ await sslStream
             }
             catch (Exception e)
             {
-                throw new SecurityException($"Failed to establish encrypted connection with server {uri}.", e);
+                throw new ServiceUnavailableException($"Failed to establish encrypted connection with server {uri}.", e);
             }
         }
     }