Parallel tests

[sergiu128]

We currently run all tests sequentially because we bind to the same set of ports throughout different tests. We can run the tests in parallel if we bind the sockets to port 0 - that would force the kernel to automatically assign the next free port for the socket.

[sergiu128]

@MaxMaeder for websocket I realize we can make a neater interface after seeing the portChan. We could do something like:

srv := &MockServer{}
go func() {
    srv.Accept()
}()
wsurl := fmt.Sprintf("localhost:%d", <-srv.PortChan)

So we can have portChan as a member of MockServer. Then once we receive on this channel it is guaranteed that there's a listener waiting for connections. This means we can also get rid of the time.Sleeps - those were there to make sure the listener instantiates before we try to connect with a client.

[sergiu128]

done in #149