[rabbitmq] Change auto-delete and exclusive defaults to `false`

Otherwise the queue will be removed when Logstash is shutdown or
restarted. In general, both attributes don't make much sense
in the context of Logstash. Also, most if not all popular
RabbitMQ clients default both attributes to `false`.

This is a breaking change so perhaps requires a more
visible change log entry.

Fixes #859.
Merge pull request #864 from michaelklishin/patch-1

[rabbitmq] Change auto-delete and exclusive defaults to `false`