core: Batch action says immediately when error occurred

lib/vagrant/batch_action.rb

@@ -89,6 +89,10 @@ module Vagrant
 
             # Store the exception that will be processed later
             Thread.current[:error] = e
+
+            # Let the user know that this process had an error early
+            # so that they see it while other things are happening.
+            machine.ui.error(I18n.t("vagrant.general.batch_notify_error"))
           end
 
           # If we forked during the process run, we need to do a hard

templates/locales/en.yml

@@ -250,6 +250,8 @@ en:
           are: %{valid_events}
 
     general:
+      batch_notify_error: |-
+        An error occurred. The error will be shown after all tasks complete.
       batch_unexpected_error: |-
         An unexpected error ocurred when executing the action on the
         '%{machine}' machine. Please report this as a bug: