'Method queries the aggregated real-time stat value for a VM.
This method should be used for aggregate counters.
:param vm_mobj: managed object of the VM
:param counter_id: id of the perf counter in VC
:param duration: in seconds from current time,
over which the stat value was applicable
:return: the aggregated stats value for the counter'

def query_vm_aggregate_stats(self, vm_mobj, counter_id, duration):

    stats = self._query_vm_perf_stats(vm_mobj, counter_id, '', duration)
    return stats.get(None, 0)
