Currently we say "done" as soon as the progress is equal to 100, however
we don't wait for the drive to be ejected/unmounted.
This commit introduces a new state, called "Finishing..." which is shown
when the progress is 100, but the drive has not been unmounted.
Currently we only pass the drive device. By passing all the object
(containing the mountpoint, size, etc) we allow more control to the
writer in how to treat the device before/during/after the burning
process.
