Initial stab at monitoring_check::cluster

initial stab at cluster check, just need to know if i'm going in right direction?
Totally. KISS to start, only add additional functionality when we need it.

for our use case, we don't need most of the check_aggregate stuff.

In fact, we will be doing our own summary (post filtering) our own filtering (to take into account  downed/silenced hosts)

If shelling out to the script works, I'm all for it. Otherwise it might actually be easier to get the raw data out of the api yourself.