Currently, /media is mounted once per boot, which causes issues
if a user need to change USB sticks, or unknowning performs an
operation that mounts /media and then needs to access a different
USB stick later (eg, updating the firmware).
To mitigate this, always unmount /media if mounted before scanning
for USB devices, so the user can choose the correct device at the
time of its use.
Additionally, add a unique exit code for user abort so we're not
treating it the same as a failure, and use it to prevent unnecessary
GUI prompts when cancelling selection of a USB device.
Signed-off-by: Matt DeVillier <matt.devillier@puri.sm>
Move code duplicated across several GUI scripts into a common
gui_functions file and include/use that.
Signed-off-by: Matt DeVillier <matt.devillier@puri.sm>
