Tests: get rid of classes in test files.

Class usage came from the unittest framework and it was always redundant
after migration to the pytest.  This commit removes classes from files
containing tests to make them more readable and understandable.

test/test_python_isolation_chroot.py

@@ -1,30 +1,29 @@
-from unit.applications.lang.python import TestApplicationPython
+from unit.applications.lang.python import ApplicationPython
 
 prerequisites = {'modules': {'python': 'any'}, 'privileged_user': True}
 
+client = ApplicationPython()
 
-class TestPythonIsolation(TestApplicationPython):
-    def test_python_isolation_chroot(self, temp_dir):
-        isolation = {'rootfs': temp_dir}
 
-        self.load('ns_inspect', isolation=isolation)
+def test_python_isolation_chroot(temp_dir):
+    client.load('ns_inspect', isolation={'rootfs': temp_dir})
 
-        assert not (
-            self.getjson(url=f'/?path={temp_dir}')['body']['FileExists']
-        ), 'temp_dir does not exists in rootfs'
+    assert not (
+        client.getjson(url=f'/?path={temp_dir}')['body']['FileExists']
+    ), 'temp_dir does not exists in rootfs'
 
-        assert self.getjson(url='/?path=/proc/self')['body'][
-            'FileExists'
-        ], 'no /proc/self'
+    assert client.getjson(url='/?path=/proc/self')['body'][
+        'FileExists'
+    ], 'no /proc/self'
 
-        assert not (
-            self.getjson(url='/?path=/dev/pts')['body']['FileExists']
-        ), 'no /dev/pts'
+    assert not (
+        client.getjson(url='/?path=/dev/pts')['body']['FileExists']
+    ), 'no /dev/pts'
 
-        assert not (
-            self.getjson(url='/?path=/sys/kernel')['body']['FileExists']
-        ), 'no /sys/kernel'
+    assert not (
+        client.getjson(url='/?path=/sys/kernel')['body']['FileExists']
+    ), 'no /sys/kernel'
 
-        ret = self.getjson(url='/?path=/app/python/ns_inspect')
+    ret = client.getjson(url='/?path=/app/python/ns_inspect')
 
-        assert ret['body']['FileExists'], 'application exists in rootfs'
+    assert ret['body']['FileExists'], 'application exists in rootfs'