Initial stab at monitoring_check::cluster

initial stab at cluster check, just need to know if i'm going in right direction?
The problem with this if the fact that this monitoring check is intended to be executed on all sensu servers.

That means sensu will make an event on failure on the sensu *host* (not the cluster) when the check returns non-zero.

You can add these to be scheduled as a montoring check, that is good.
But the check itself must always return 0 unless it really can't connect to the api or something.

Does that make sense? The return code of check_cluster.rb must reflect the output of the script itself, *not* the health status of the cluster.

The health status of the cluster must be sent out via the secondary channel, localhost:3030.