GlusterFS: Check for groups in template file

roles/openshift_storage_glusterfs/templates/glusterfs.conf.j2

@@ -2,7 +2,7 @@
 dm_thin_pool
 dm_multipath
 target_core_user
-{% if inventory_hostname in groups.glusterfs or inventory_hostname in groups.glusterfs_registry %}
+{% if (groups.glusterfs is defined and inventory_hostname in groups.glusterfs) or (groups.glusterfs_registry is defined and inventory_hostname in groups.glusterfs_registry) %}
 dm_snapshot
 dm_mirror
-{% endif %}
+{% endif %}