This changes the method used to poll xenserver for bandwidth data.
The reccomended way of collecting such data from xenserver (namely the
RRD files provided by the hosts) do not seem to be reliable, they
will sometimes be correct, often will be signifigantly under (> 10%),
and occasionally will show artifacts, such as phantom 4gb bandwidth
'spikes'.
This patch changes that to use the much simpler method of simply polling the
byte counters on the VIF network devices on the host. (We have old non-nova
code that does that on xenserver, and that method is known to work).
This should also make it much easier for other hypervisors other than
xenserver to implement bandwidth polling, as polling the counters is a rather
more universal method.
Fixes bug 1055737
Change-Id: I6a280d8bbfcc74914f888b11bc09349a270a5f58
e6de054235