[Device Notifier] Auto-hide popup after device is unmounted

Summary:
When unmounting a removable device from dolphin, the device notifier
will popup saying the device can now be safely removed. But the popup
never auto-hides.

Test Plan:
Plug a USB pen drive
Unmount it from dolpin
Device notifier should popup and hide itself after 3 seconds

Reviewers: #plasma, #vdg, broulik

Reviewed By: #plasma, broulik

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D16045

applets/devicenotifier/package/contents/ui/devicenotifier.qml

@@ -192,6 +192,7 @@ Item {
 
                 if (sdSource.isViableDevice(lastUdi)) {
                     plasmoid.expanded = true
+                    plasmoid.fullRepresentationItem.spontaneousOpen = true;
                 }
             }
         }