Discarding state works with VBoxManage

lib/vagrant/action/vm/discard_state.rb

@@ -11,7 +11,7 @@ module Vagrant
         def call(env)
           if env[:vm].state == :saved
             env[:ui].info I18n.t("vagrant.actions.vm.discard_state.discarding")
-            env[:vm].vm.discard_state
+            env[:vm].driver.discard_saved_state
           end
 
           @app.call(env)

lib/vagrant/driver/virtualbox.rb

@@ -107,6 +107,11 @@ module Vagrant
         end
       end
 
+      # Discards any saved state associated with this VM.
+      def discard_saved_state
+        execute("discardstate", @uuid)
+      end
+
       # Executes a raw command.
       def execute_command(command)
         raw(*command)