Add Ganglia slowmon timeout based on "TN" field in ganglia data
Ganglia mon daemon can sometimes keep reporting a value of a metric on its port 8016 very long after the last value was received. There is an attribute named "TN" in the metric data that tells how many seconds have passed since the value was received. Use this as a timeout on the ganglia-derived slowmon variables. There is also a TN attribute to the HOST element in the port 8016 ganglia data, which seems to be the time elapsed since anything was received from the host; this could be used for an overall host up/down metric.