Refactoring long polling transport to be able to fix bug #3227

Before it was easier because we mocked the transport helper. Now that the `ProcessResponse` method has been moved to the ClientTransportBase class it would require mocking the whole transport. Note that this test is for the store `WebsocketTransport` where we can't use Moq so just creating a mock transport with `CallBase = true` is not an option. I could potentially verify the message that is passed to the Trace method but did not think it was worth it. We do have end to end tests which would fail if the message was not passed correctly to the `ProcessResponse` method so we still have coverage.