Cosmetic bug fix in admin interface

When deleting a trunk, the return from call_vland() is the trunk_id,
not a port_id. Fix this and remove a python error.

Change-Id: Id81efba38e1057de8f1479534c26582117189d94
diff --git a/admin.py b/admin.py
index 38d123c..ca13a0d 100755
--- a/admin.py
+++ b/admin.py
@@ -556,7 +556,7 @@
         exitcode = Error.NOTFOUND
 elif args.which == 'delete_trunk':
     try:
-        port_id = call_vland('db_update',
+        trunk_id = call_vland('db_update',
                              {'command':'db.delete_trunk',
                               'data': {'trunk_id': args.trunk_id}})
         print 'Deleted trunk_id %s' % trunk_id