Fix example XRootD groupname auth for VOMS FQANs

[brianhlin]

We get it right in the example here https://opensciencegrid.org/docs/data/xrootd/xrootd-authorization/#authorization-database. From Wei:

XrdVoms maps a typical VOMS attributes

VO: atlas <-- o:
VO group: /atlas/usatlas <- g:

You have also have self defined "Special Compound ID"s, for example

= atlprod o: atlas g: /atlas r: production
This define "atlprod" as VO "atlas", VO group "/atlas", Role "production"

x atlprod /xrootd/atlas rwildn
This define what access privilege "atlprod" has

The auth file are evaluated in order. The first match will be picked up.

[matyasselmeci]

Aha!

We get it right in osg-test, too.