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

https://jira.spring.io/browse/AMQP-447

I have signed and agree to the terms of the SpringSource Individual Contributor License Agreement
I don't think that this is good warn. I really can prefer to configure my `CF` using just `addresses` with single value, e.g. `load-balancer` URL.