setup.py: add xcat.conf.example (#526)

File was missing from data_files and as such not packaged.

Fixes #526.

Author: thiell

setup.py

@@ -46,6 +46,7 @@
                   (os.path.join(CFGDIR, 'groups.conf.d'),
                    ['conf/groups.conf.d/genders.conf.example',
                     'conf/groups.conf.d/slurm.conf.example',
+                    'conf/groups.conf.d/xcat.conf.example',
                     'conf/groups.conf.d/README']),
                   (os.path.join(CFGDIR, 'groups.d'),
                    ['conf/groups.d/cluster.yaml.example',