break VTNNetwork and VTNPort out into a library file

Change-Id: I56c74b4041af09ce9b62a9e6328795156c91fc09
diff --git a/xos/vtn-onboard.yaml b/xos/vtn-onboard.yaml
index 9141dbd..edee561 100644
--- a/xos/vtn-onboard.yaml
+++ b/xos/vtn-onboard.yaml
@@ -15,6 +15,7 @@
           # base_url is non-null.
           models: models.py
           admin: admin.py
+          django_library: vtnnetport.py
           admin_template: templates/vtnadmin.html
           synchronizer: synchronizer/manifest
           synchronizer_run: vtn-synchronizer.py