BRUSSELS — Last year’s gathering of Europe’s far right in Brussels took place behind metal shutters after protesters, police and city politicians tried to stop it from going ahead . This year, the doors are wide open — albeit flanked by security guards — and it’s the EU’s mainstream leadership that is under siege. Just a day after the EU was rocked by the arrest of two senior figures in a corruption probe , many at the Battle for the Soul of Europe conference — hosted by MCC Brussels, a think