udisks2: add support for 'safely removing storage'

mountutils lacks implemention of ejecting storage on Linux.
Add that to our own code (not to mountutils as it is hard to
do DBus calls from there).

src/downloadthread.cpp

@@ -775,7 +775,14 @@ void DownloadThread::_writeComplete()
 #endif
 
     if (_ejectEnabled)
+    {
         eject_disk(_filename.constData());
+#ifdef Q_OS_LINUX
+        /* mountutils only implemented unmount and not eject on Linux. Do so through udisks2 */
+        UDisks2Api udisks;
+        udisks.ejectDrive(_filename);
+#endif
+    }
 
     emit success();
 }