If VSG module does not exist, then do not try to list tenants
If VSG module does not exist, then do not try to list tenants

Change-Id: I043e76259422e7ebef06a257ce9e9637db108c9f

leejieyu/vtn2.0,leejieyu/vtn2.0,leejieyu/vtn2.0,leejieyu/vtn2.0