Update gmetad.conf and add custom RRAs

I have updated gmetad.conf from the ganglia repo and added custom RRAs with default params. I have also changed the gmetad.conf template to remove el6 from the filename (as it's used as a common template across all supported OSes)
Ok, I'll add a param for this. el6 should use this without a problem (I use case_sensitive_hostnames 0 on my setup)