Adds more enrichers/attributes to cassandra node/cluster

Things still to do are:
* thrift-port-lateny-windowed reports as 0 until thrift-port-latency is non-null. This will mess with the averaging at the cluster level of the thrift-port-lateny-windowed.
* standard JMX metrics (e.g. cpu usage etc) are not coming through. I first need to retest on a clean install on AWS (rather than re-using machines).

Note that I changed the value for "unavailable sensors" from -1 to null, so that it wouldn't interfere with calculations of averages at the cluster.