Fix create_vlan args

Change-Id: Ibbec0235d1428ea888c5bc3a53721129c8741f3d
diff --git a/admin.py b/admin.py
index 77a1556..fc0e056 100644
--- a/admin.py
+++ b/admin.py
@@ -322,7 +322,7 @@
                               'data':
                               {'name': opts.create_vlan[0],
                                'tag': opts.create_vlan[1],
-                               'is_base_vlan': opts.create_vlan[2]}})
+                               'is_base_vlan': is_positive(opts.create_vlan[2])}})
         print 'Created vlan_id %d' % vlan_id
     except InputError as inst:
         print 'Failed: %s' % inst