fix config, add access level parameter for ipmitool

There were errors in the config file - the parameters needed to be grouped inside of the module {} section.  Also, I added a parameter for the user access level in ipmitool, since it defaults to ADMIN and my cluster uses a non-privileged user for IPMI monitoring.

Original code was using 'params' as a global, which didn't work in the context of being run from gmond.  Fixed that, and had to hard-code the ipmi_ prefix in one place.  But it works now.