core: don't load vagrantfile on plugin command

CHANGELOG.md

@@ -25,6 +25,8 @@ BUG FIXES:
   - core: 100% CPU spike when waiting for SSH is fixed. [GH-2401]
   - core: Command lookup works on systems where PATH is not valid UTF-8 [GH-2514]
   - core: Human-friendly error if box metadata.json becomes corrupted. [GH-2305]
+  - core: Don't load Vagrantfile on `vagrant plugin` commands, allowing
+    Vagrantfiles that use plugins to work. [GH-2388]
   - guests/freebsd: Mounting NFS folders works. [GH-2400]
   - guests/freebsd: Uses `sh` by default for shell. [GH-2485]
   - guests/redhat: Down interface before messing up configuration file

bin/vagrant

@@ -64,7 +64,11 @@ opts[:ui_class] ||= Vagrant::UI::Colored
 # of the plugin interface.
 ARGV.each do |arg|
   if !arg.start_with?("-")
-    ENV["VAGRANT_NO_PLUGINS"] = "1" if arg == "plugin"
+    if arg == "plugin"
+      ENV["VAGRANT_NO_PLUGINS"] = "1"
+      ENV["VAGRANT_VAGRANTFILE"] = "plugin_command_#{Time.now.to_i}"
+    end
+
     break
   end
 end

lib/vagrant/environment.rb

@@ -67,7 +67,7 @@ module Vagrant
         :local_data_path  => nil,
         :lock_path        => nil,
         :ui_class         => nil,
-        :vagrantfile_name => nil
+        :vagrantfile_name => nil,
       }.merge(opts || {})
 
       # Set the default working directory to look for the vagrantfile