mark memcached connections as nonpersistent

bitrix tries to instantiate persistet connection by default. I've just observed on bomondceramica.ru that it might lead to hundreds connections from single php-fpm worker to memcached instance, and total number of connection might drain the whole memcached pool (which 1024 connections by default). Not sure if this is an issue with bomondceramica.ru, bitrix driver in general but let's disable it by default.