Fix LXC 3.0 compatibility with old boxes

Creating a new vagrant machine with a box created with an old LXC config
format would fail with LXC 3.0. We now update the LXC config of the box
itself before calling `lxc-create`.

lib/vagrant-lxc/action/create.rb

@@ -25,7 +25,11 @@ module Vagrant
           end
           driver = env[:machine].provider.driver
           template_options = env[:lxc_template_opts]
-          if ! driver.supports_new_config_format
+          if driver.supports_new_config_format
+            if env[:lxc_box_config]
+              driver.update_config_keys(env[:lxc_box_config])
+            end
+          else
             template_options['--oldconfig'] = ''
           end
           driver.create(

lib/vagrant-lxc/action/handle_box_metadata.rb

@@ -33,8 +33,10 @@ module Vagrant
           end
 
           if template_config_file.exist?
+            @env[:lxc_box_config] = template_config_file.to_s
             @env[:lxc_template_opts].merge!('--config' => template_config_file.to_s)
           elsif old_template_config_file.exist?
+            @env[:lxc_box_config] = old_template_config_file.to_s
             @env[:lxc_template_config] = old_template_config_file.to_s
           end
 

lib/vagrant-lxc/driver.rb

@@ -249,8 +249,9 @@ module Vagrant
         write_config(contents)
       end
 
-      def update_config_keys
-        @cli.update_config(config_path)
+      def update_config_keys(path = nil)
+        path = path || config_path
+        @cli.update_config(path)
       rescue Errors::ExecuteError
         # not on LXC 2.1+. Doesn't matter, ignore.
       end