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: I994053b8b18c1de0439242aa45bdf38e5abba630
diff --git a/xos/admin.py b/xos/admin.py
index 92fa51d..863bf55 100644
--- a/xos/admin.py
+++ b/xos/admin.py
@@ -57,6 +57,7 @@
 
     class Meta:
         model = VSGService
+        fields = '__all__'
 
 class VSGServiceAdmin(ReadOnlyAwareAdmin):
     model = VSGService
@@ -129,6 +130,7 @@
 
     class Meta:
         model = VSGTenant
+        fields = '__all__'
 
 class VSGTenantAdmin(ReadOnlyAwareAdmin):
     list_display = ('backend_status_icon', 'id', 'subscriber_tenant' )