Initial stab at monitoring_check::cluster

initial stab at cluster check, just need to know if i'm going in right direction?
What is missing here is the *extra* part. The part where the output of the actual check is sent to the localhost socket with the real output data. 

This is important because the "source" must be masked to be the cluster name.

In the end, this function must return ok by default, and let a normal ruby exception (or rescue) return non-0. Regardless of the output of the check.

The output of the check has to be actually sent to localhost:3030