Break up finding non-installed plugins into separate function.

vagrant/.vagrantplugins.rb → vagrantplugins.rb

-# -*- mode: ruby -*-
-# vi: set ft=ruby :
-
 def install_plugins(plugins)
-  not_installed = []
-  plugins.each do |plugin|
-    unless Vagrant.has_plugin?(plugin)
-      not_installed << plugin
-    end
-  end
-
+  not_installed = get_not_installed plugins
   if not_installed.any?
     puts "The following required plugins must be installed:"
     puts "'#{not_installed.join("', '")}'"
@@ -22,6 +13,16 @@ def install_plugins(plugins)
   end
 end
 
+def get_not_installed(plugins)
+  not_installed = []
+  plugins.each do |plugin|
+    unless Vagrant.has_plugin?(plugin)
+      not_installed << plugin
+    end
+  end
+  return not_installed
+end
+
 def install_plugin(plugin)
   system "vagrant plugin install #{plugin}"
 end