Method on_connection_open

cpp/src/container_test.cpp:520–533

    test_mt_handler_wq() : wq_(0) {}

    void on_connection_open(proton::connection &c) override {
        {
            std::unique_lock<std::mutex> l(wqlock_);
            // Just record first connection side, inbound or outbound
            if (!connection_) {
                connection_ = c;
                wq_ = &c.work_queue();
                call_do_close_ = make_work(&test_mt_handler_wq::do_close, this);
            }
            else
                return;
        }
        test_mt_handler::on_connection_open(c);
    }
    void initiate_close() {
        std::unique_lock<std::mutex> l(wqlock_);
        wq_->add(call_do_close_);