Enable Selective Routing of Events

[acharlieh]

In the cookbook we currently allow multiple clusters to be defined, and we route events to all of them. It would be nice if we could additionally define additional clusters and route events selectively to them.

We probably should look into defining "my_cluster" as a single string (breaking it out of the assumed first element of "clusters". And then have an "inactive_clusters" or "additional_clusters" that we could route events to.