providers/docker: Get rid of some explicit requires in favor of autoloading

plugins/providers/docker/action/prepare_nfs_settings.rb

@@ -1,5 +1,3 @@
-require_relative '../errors'
-
 module VagrantPlugins
   module DockerProvider
     module Action

plugins/providers/docker/errors.rb

@@ -1,5 +1,3 @@
-require 'vagrant/errors'
-
 module VagrantPlugins
   module DockerProvider
     module Errors

plugins/providers/docker/plugin.rb

@@ -1,5 +1,9 @@
 module VagrantPlugins
   module DockerProvider
+    autoload :Action, File.expand_path("../action", __FILE__)
+    autoload :Driver, File.expand_path("../driver", __FILE__)
+    autoload :Errors, File.expand_path("../errors", __FILE__)
+
     class Plugin < Vagrant.plugin("2")
       name "docker-provider"
 

plugins/providers/docker/provider.rb

@@ -1,8 +1,5 @@
 require "log4r"
 
-require_relative 'driver'
-require_relative 'action'
-
 module VagrantPlugins
   module DockerProvider
     class Provider < Vagrant.plugin("2", :provider)