roles/nginx: Ensure minimal server is the fallback server

roles/nginx/templates/nginx-hostname-vhost.conf.j2

 server {
-    listen       80;
-    listen       [::]:80;
-    server_name  {{ inventory_hostname }};
+    listen       80 default_server;
+    listen       [::]:80 default_server;
     root         /srv/http;
 
     include snippets/letsencrypt.conf;
 
-	location / {
-		return 404;
-	}
+    location / {
+        return 404;
+    }
 }