Adds Support for Mirrored Queues within a cluster.

Prior to this patch, mirrored queues would not behave properly.
Rabbit mirrored queues had several bugs that were fixed in 2.8.7:
  https://www.rabbitmq.com/release-notes/README-2.8.7.txt

rabbitmq::repo::apt can not be used since 2.8.7 is not the latest version:
  http://www.rabbitmq.com/install-debian.html

The patch adds a new paramater [*config_mirrored_queues*] that will install
the rabbitmq-server 2.8.7 package and required dependencies when
config_cluster is true.
Merge pull request #55 from danehans/master

Add support for Mirrored Queues within a Rabbit Cluster