fix proxy object deletion in tests

Change-Id: I02917d236925fc433b95c2d187e6fdc1deaa90fb
diff --git a/xos/tests/api/hooks.py b/xos/tests/api/hooks.py
index 248907b..ff9b88c 100644
--- a/xos/tests/api/hooks.py
+++ b/xos/tests/api/hooks.py
@@ -165,7 +165,7 @@
 
 
 def deleteTruckrolls():
-    for s in VTRTenant.objects.all():
+    for s in VTRTenant.get_tenant_objects().all():
         s.delete(purge=True)