Django 1.8 fails with an ImproperlyConfigured exception when `fields` or
`exclude` isn't set:

```
class Meta:
 fields = '__all__'
```

on all descendents of ModelForm.

Omitting this is deprecated in 1.7:

https://docs.djangoproject.com/en/1.7/topics/forms/modelforms/#selecting-the-fields-to-use

Change-Id: I3cba9ab7f3e37e481d55d36ded1ee4ddb8c3ecf0
diff --git a/xos/admin.py b/xos/admin.py
index cf5dfa6..dce13e8 100644
--- a/xos/admin.py
+++ b/xos/admin.py
@@ -79,6 +79,8 @@
 
     class Meta:
         model = VOLTTenant
+        fields = '__all__'
+
 
 class VOLTTenantAdmin(ReadOnlyAwareAdmin):
     list_display = ('backend_status_icon', 'id', 'service_specific_id', 's_tag', 'c_tag', 'subscriber_root' )
@@ -208,6 +210,7 @@
 
     class Meta:
         model = CordSubscriberRoot
+        fields = '__all__'
 
 class CordSubscriberRootAdmin(ReadOnlyAwareAdmin):
     list_display = ('backend_status_icon', 'id',  'name', )