1. host/uptime, disk/io_time and disk/weighted_io should be
counter/cumulative metrics. SO we have to use the Sum aggregation method
rather than LastValue aggregation method (which will declare the metric
as gauge metric).
2. Renamed label "device" for disk/* metrics to "device_name".
This is to clarify that it is device_name (sda1) rather than device_path
(/dev/sda1)
Host collector report three things today:
1. Host OS uptime (in seconds)
2. Host kernel version (as a metric label)
3. Host OS version (as a metric label)
