Added the option to define rabbitmq's queues as "durable"

Due to its nature, RabbitMQ data is very volatile.
Since messaging is all about speed and amounts of data,
all the messages are kept in RAM unless you define
queues as "durable", which will make RabbitMQ write them
to disk. This is actually supported by OpenStack with
the setting amqp_durable_queues=True in nova.conf.

Change-Id: I854970b8a6d5e771f8bd4410cb3bcf6bf705cee7
Implements: blueprint add-rabbit-durable-queues-param
Merge "Added the option to define rabbitmq's queues as "durable""