The previous syntax was severely limited in its options

  -usbdevice disk:/home/berrange/output.img

The new syntax is the same as for other disk types

  -drive file=/home/berrange/output.img,if=none,id=usb-1,index=1
  -device usb-storage,drive=usb-1

Again, the index= arg is wrong here, and will be removed in a
later merge