get scsi product id and serial number for block devices

[agrover]

We wouldn't actually use this for anything, but if a blockdev is missing both the device path(e.g. /dev/sdc) and the Froyo block guid are both pretty meaningless when we want to let the user know we are missing a drive, and it is this one. We can include it in the saved block device metadata (we most need to have it when we can no longer access the drive)