Check for redir before forwarding ports

Make a system call out to `which` to see if redir exists on the PATH
before trying to forward ports.  Raises a VagrantError if it does not.

lib/vagrant-lxc/action/forward_ports.rb

@@ -26,7 +26,12 @@ module Vagrant
 
           if @env[:forwarded_ports].any?
             env[:ui].info I18n.t("vagrant.actions.vm.forward_ports.forwarding")
+
+            if redir_installed?
               forward_ports
+            else
+              raise Errors::RedirNotInstalled
+            end
           end
         end
 
@@ -79,6 +84,10 @@ module Vagrant
             pid_file.write(redir_pid)
           end
         end
+
+        def redir_installed?
+          system "sudo which redir"
+        end
       end
     end
   end

lib/vagrant-lxc/errors.rb

@@ -17,6 +17,9 @@ module Vagrant
       class IncompatibleBox < Vagrant::Errors::VagrantError
         error_key(:lxc_incompatible_box)
       end
+      class RedirNotInstalled < Vagrant::Errors::VagrantError
+        error_key(:lxc_redir_not_installed)
+      end
     end
   end
 end

locales/en.yml

@@ -40,3 +40,6 @@ en:
       lxc_template_file_missing: |-
         The template file used for creating the container was not found for %{name}
         box.
+
+      lxc_redir_not_installed: |-
+        `redir` is not installed or is not accessible on the PATH.