List plugins should have output when no plugins

plugins/commands/plugin/action/list_plugins.rb

@@ -40,8 +40,12 @@ module VagrantPlugins
           end
 
           # Output!
-          installed_map.values.each do |spec|
-            env[:ui].info "#{spec.name} (#{spec.version})"
+          if installed_map.empty?
+            env[:ui].info(I18n.t("vagrant.commands.plugin.no_plugins"))
+          else
+            installed_map.values.each do |spec|
+              env[:ui].info "#{spec.name} (#{spec.version})"
+            end
           end
 
           @app.call(env)

templates/locales/en.yml

@@ -417,6 +417,8 @@ en:
           the comments in the Vagrantfile as well as documentation on
           `vagrantup.com` for more information on using Vagrant.
       plugin:
+        no_plugins: |-
+          No plugins installed.
         installing: |-
           Installing the '%{name}' plugin. This can take a few minutes...
         uninstalling: |-