svlogd : config file directory fix / log directory has an attribut

Actually the config file for svlogd is not in the good place, so that svlogd can't be configured.
My patches fix that, 
I also add the possibility to choose with an attribute named syslog_dir, the path of the default log files. No more '/var/log' hardcoded. The default svlogd behaviour has been hardcoded when no syslog_dir attrbute has been definned.