This patch changes how media-change is detected to use a mechanism more
similar to what 'popular' OSes use.

The motive for this change is that more and more emulated-SCSI devices
(sbp2, usb-storage, etc) don't support START_STOP unless they need it.
Other OSes won't send a START_STOP unless the device reports NOT_READY,
indicating that it needs an explicit command to start up.

One could argue that these devices are out-of-spec, but they are so common
that they basically define the de facto spec.

Basically, any device that needs a START_STOP should still get it, but ones
that don't need it won't.