Add some basic driver methods for configuring disks

plugins/providers/virtualbox/cap/configure_disks.rb

@@ -9,6 +9,20 @@ module VagrantPlugins
         def self.configure_disks(machine, defined_disks)
           return nil if defined_disks.empty?
         end
+
+        protected
+
+        # Maybe move these into the virtualbox driver??
+        # Versioning might be an issue :shrug:
+
+        def current_vm_disks(driver)
+        end
+
+        def vmdk_to_vdi(driver)
+        end
+
+        def vdi_to_vmdk(driver)
+        end
       end
     end
   end