Allow to make AMQP queues persistent

[lennartkoopmann]

A reminder for the new radio version:

When you declare a queue with rabbit you can denote whether you want the
messages to be "persistent" ie: flushed to disk ( although this isn't guaranteed* ). In
python it's the "delivery_mode" setting and in java it's "MessageProperties". It's
something that can have an adverse affect on performance if you don't care
about/need that I/O done. There's some raw numbers here:
http://www.rabbitmq.com/blog/2012/04/25/rabbitmq-performance-measurements-part-2/ .

[cloax]

Thanks for taking it under consideration! -joe

[lennartkoopmann]

This is now part of #220