fixes 4 issues:
* use correct /api2/ext url to get the 'success' parameter
* check 'used' property for 'unused' (pbs vs pve)
* use 'name' instead of 'devpath' for id
(name always contains the correct id for the product,
e.g. /dev/sdd for pve and sdd for pbs)
* add a reload in taskDone to reload the list of disks when the inti is done