use /var/run for fpm pid files

currently /var/run/php is cleaned up by php session cleanup script
which cleans up everything in that dir, not only php session files

so as consequence this removes php-fpm pidfiles and service restart
remains confused what to stop.

php-wsdl cache files get nuked by the same problem, so those could be
moved to /var/cache/php, so they could survive reboots

probably it's wrong to have /var/run/php as php-session storage (note
the generic namem it's not /var/run/php/sessions etc), but changing that
would need more efforts, as need to support old and new configuration,
and each php sapi could have different config (they have different
php.ini (or equivalent) files)