Implement proper removal of cloned disk

Author: Emerson Prado

lib/vagrant/disksize/actions.rb

@@ -44,7 +44,7 @@ def ensure_disk_resizable(env)
             unless File.exist? new_disk[:file]
               clone_as_vdi(driver, old_disk, new_disk)
               attach_disk(driver, new_disk)
-              File.delete(old_disk[:file])
+              remove_disk(driver, old_disk)
             end
           end
         end
@@ -81,6 +81,10 @@ def attach_disk(driver, disk)
           driver.execute('storageattach', @machine.id, '--storagectl', controller, '--port', port, '--device', device, '--type', 'hdd',  '--medium', disk[:file])
         end
 
+        def remove_disk(driver, disk)
+          driver.execute("closemedium", disk[:file], '--delete')
+        end
+
         def get_disk_size(driver, disk)
           size = nil
           driver.execute('showmediuminfo', disk[:file]).each_line do |line|