nixos/test-driver: fix resource cleanup of vlan/qmp objects

Using __del__ is somewhat unsound resource cleanup in our clase the
logger already closed its logfile and therefor fails with exception
before the rest of the resources can be cleaned up.

nixos/lib/test-driver/test_driver/driver.py

@@ -99,7 +99,16 @@ class Driver:
         with self.logger.nested("cleanup"):
             self.race_timer.cancel()
             for machine in self.machines:
-                machine.release()
+                try:
+                    machine.release()
+                except Exception as e:
+                    self.logger.error(f"Error during cleanup of {machine.name}: {e}")
+
+            for vlan in self.vlans:
+                try:
+                    vlan.stop()
+                except Exception as e:
+                    self.logger.error(f"Error during cleanup of vlan{vlan.nr}: {e}")
 
     def subtest(self, name: str) -> Iterator[None]:
         """Group logs under a given test name"""

nixos/lib/test-driver/test_driver/machine.py

@@ -1234,6 +1234,9 @@ class Machine:
         self.monitor.close()
         self.serial_thread.join()
 
+        if self.qmp_client:
+            self.qmp_client.close()
+
     def run_callbacks(self) -> None:
         for callback in self.callbacks:
             callback()

nixos/lib/test-driver/test_driver/qmp.py

@@ -49,7 +49,7 @@ class QMPSession:
         sock.connect(str(path))
         return cls(sock)
 
-    def __del__(self) -> None:
+    def close(self) -> None:
         self.sock.close()
 
     def _wait_for_new_result(self) -> dict[str, str]:

nixos/lib/test-driver/test_driver/vlan.py

@@ -59,7 +59,7 @@ class VLan:
 
         self.logger.info(f"running vlan (pid {self.pid}; ctl {self.socket_dir})")
 
-    def __del__(self) -> None:
+    def stop(self) -> None:
         self.logger.info(f"kill vlan (pid {self.pid})")
         self.fd.close()
         self.process.terminate()