Set appropriate policy for mirrored queues

Previously, the config_mirrored_queues parameter
had no effect. This patch adds a policy defined type
and if mirroring is requested, an appropriate
policy is created. The README has been updated to
clarify the case where this is applicable.
Set HOME env variable to nil when leveraging rabbitmq to remove type error from Python script
Merge pull request #205 from bezerker/master

Resolve rabbitmq_exchange type error
Merge pull request #171 from michaeltchapman/mirrorqueue

Set appropriate policy for mirrored queues