Method initiate_close

cpp/src/container_test.cpp:534–537

        test_mt_handler::on_connection_open(c);
    }
    void initiate_close() {
        std::unique_lock<std::mutex> l(wqlock_);
        wq_->add(call_do_close_);
    }
    void do_close() { connection_.close(); }
    void on_connection_close(proton::connection &) override { set("closed"); }
};