Remove network_event_loop instance in close()
Remove network_event_loop instance in close()

The asyncio.new_event_loop() instance is now removed from the NetworkThread
class during shutdown. This enables a NetworkThread instance to be restarted
after being closed. The current NetworkThread class guards against an existing
new_event_loop during initialization.


Former-commit-id: 036441728cfeffbac012f160f1e083b943bb383d
syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin2,syscoin/syscoin