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

https://jira.spring.io/browse/AMQP-447

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Hi @artembilan,

True, for RabbitMQ client library this could be a breaking change, but if using via spring-amqp it should be OK. However, the behavior for the empty string passed is not specified in both projects.

The thing is that currently the spring-amqp code/behavior is counter-intuitive.
If not looking closely into the parseAddresses() function one might assume that the addresses property overrides host+port only if not empty.
Unfortunately, parseAddresses() never returns an empty array, so addresses overrides host *always*.