Assume interface detach called for port not found

If the interface has been detached before we call
detach_interface, then we keep on calling it as we
get a 404 from nova. Let's assume it's being called
and check if the interface has been detached.

Task: 42195

Change-Id: I768eeb10c2c24a0c93749b11636ef3e003ecfcd9

heat/engine/clients/os/nova.py

@@ -788,7 +788,7 @@ echo -e '%s\tALL=(ALL)\tNOPASSWD: ALL' >> /etc/sudoers
             server = self.fetch_server(server_id)
             if server:
                 server.interface_detach(port_id)
-                return True
+        return True
 
     def interface_attach(self, server_id, port_id=None, net_id=None, fip=None,
                          security_groups=None):

heat/tests/openstack/nova/test_server.py

@@ -5165,7 +5165,7 @@ class ServerInternalPortTest(ServersTest):
         server.client().servers.get.return_value = nova_server
 
         server.prepare_for_replace()
-        check_detach.assert_not_called()
+        self.assertEqual(3, check_detach.call_count)
         self.assertEqual(0, self.port_delete.call_count)
 
     def test_prepare_ports_for_replace_error_state(self):