AMQP-422 PublisherCallbackChannel: postpone close

JIRA: https://jira.spring.io/browse/AMQP-422

Add `stopSemaphore` and `closeTimeout` option to the `PublisherCallbackChannelImpl`
to postpone physical `close` until timeout or handlong for all pending confirms

Decrease `@Repeat` for `RabbitTemplatePerformanceIntegrationTests` for better build performance
How about something like...

    try {
        wFCOD();
    }
    catch (InterruptedException) {
        Thread.currentThread().interrupt();
    }
    if (channel.isOpen()) {
        try {
            channel.close();
        }
        catch (AlreadyClosedException e) {}
    }

??