Implementation of Rackspace Queues monitoring

Implementation of Rackspace Queues monitoring - please do clean up the version and download_url, depending on the direction taken for https://github.com/newrelic-platform/newrelic_rackspace_load_balancers_plugin/pull/8.

Thanks in advance for merging these PRs and getting Rackspace Queues-monitoring implemented in the newrelic-platform/newrelic_plugins_chef cookbook!

Kind regards,
David