[tests] Call super() in tearDownClass methods

Not doing this causes issues:
https://docs.djangoproject.com/en/3.1/topics/testing/tools/#django.test.SimpleTestCase.databases

Author: nemesifier

install-dev.sh

@@ -1,2 +1,6 @@
 #!/bin/bash
 set -e
+# TODO: can be remove when openwisp-users 0.4.1 is released
+# Commit needed for failures in tests:
+# https://github.com/openwisp/openwisp-users/commit/ef347927136ddb4676479cb54cdc7cd08049e2e5
+pip install -U --no-deps https://github.com/openwisp/openwisp-users/tarball/master

openwisp_controller/config/tests/test_admin.py

@@ -896,4 +896,5 @@ def test_clone_template(self):
 
     @classmethod
     def tearDownClass(cls):
+        super().tearDownClass()
         devnull.close()

openwisp_controller/connection/tests/test_ssh.py

@@ -26,6 +26,7 @@ def setUpClass(cls):
 
     @classmethod
     def tearDownClass(cls):
+        super().tearDownClass()
         cls.mock_ssh_server.__exit__()
 
     def test_connection_connect(self):