Virtual disks not excluded when in pool mode

[jintakhan]

I have a virtualized TNS instance that has an array of hard drives run via a HBA passthrough augmented by a virtio virtual disk used as an L2ARC vdev. But the virtual disk, which is prefixed vdX, is not excluded when this script tries to spin the array down. This is less consequential than #39 as these virtual disks don't support SMART to begin with, but does throw some small errors in logger.