AMQP-447 Ignore empty string passsed to AbstractConnectionFactory.setAddresses()

https://jira.spring.io/browse/AMQP-447

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He-he! Good catch!

So, I see now you point: if we provide an empty `addresses` we do fallback to the `host/port`. Right?
In this case we should say some `info`, at least, to notify user that his `empty string` is ignored.