Clear TestNode objects after shutdown
Clear TestNode objects after shutdown

TestNode objects need to be removed during shutdown, as setup_nodes does not
remove previous TestNode objects from previous test runs during setup.


Former-commit-id: fb72df4a6922ba9790ce80ea9f1770aeeaa4019d
syscoin/syscoin2,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin2,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin