'Method queries the real-time stat values for a VM, for all devices.
This method should be used for device(non-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: a map containing the stat values keyed by the device ID/name'

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

    stats = self._query_vm_perf_stats(vm_mobj, counter_id, '*', duration)
    stats.pop(None, None)
    return stats
