Fix the path of PIDFILE for Ubuntu/Debian

The PIDFILE is pointing to `/var/run/redis.pid` on Ubuntu/Debian but the path used in the initscript is `/var/run/redis/redis-server.pid`.

This misconfiguration creates a bug of restarting `redis-server` service at every Puppet pull because the command `/etc/init.d/redis-server status` checks for the wrong PIDFILE and always return false.