increase nuke_limit to prevent 503 error 'FetchError c Could not get storage'.

slapos/recipe/generic_varnish/template/varnishd.in

@@ -4,6 +4,7 @@ DAEMON_OPTS="-F \
              -a %(varnish_ip)s:%(varnishd_server_port)s \
              -T %(varnish_ip)s:%(varnishd_manager_port)s \
              -t 0 \
+             -p nuke_limit=500 \
              -n %(varnish_instance_name)s \
              -f %(vcl_file)s \
              -s file,%(varnish_data)s/varnish_storage.bin,1G"