Register a middleware action from within a plugin

lib_vagrant_plugin_v1.rb.patch

index 0b10045..be73523 100644
--- a/lib/vagrant/plugin/v1.rb
+++ b/lib/vagrant/plugin/v1.rb
@@ -114,6 +114,10 @@ module Vagrant
         data[:provisioners]
       end
 
+      def self.action(stack, &block)
+        Vagrant.actions[stack.to_sym].instance_eval(&block)
+      end
+
       # Registers the plugin. This makes the plugin actually work with
       # Vagrant. Prior to registering, the plugin is merely a skeleton.
       def self.register!(plugin=nil)

my_plugin.rb

class Plugin < Vagrant.plugin("1")
  # ... includes, name, description ...

  # push my middleware on the start stack
  action(:start) {
    use MyAction
  }
end