Openstack reports in/out byte rates for each vm and for each device
on those VMs, but I aggregate the per-device stats into per-VM in/out
totals.

Currently, I'm reporting these API calls:
  * (network,subnet,port,router).(create,update,delete)
  * (image).(upload,update)
API calls are reported from which "host" they were issued (I think);
if there is no host info logged (like for images), the hostname is
"null".