Tests: ensure temporary directories and files are removed after tests

- QSettings object needs special care, as file was re-created on exit
- Append a cleanup function as soon as possible to ensure temporary dirs & files are removed in any case
- prefer addCleanup() over tearDown(), keeping creation and cleanup together

test/test_bytes2human.py

@@ -1,6 +1,5 @@
 import os.path
 import shutil
-import sys
 import tempfile
 
 from test.picardtestcase import PicardTestCase
@@ -13,15 +12,10 @@ class Testbytes2human(PicardTestCase):
     def setUp(self):
         super().setUp()
         # we are using temporary locales for tests
-        self.tmp_path = tempfile.mkdtemp()
-        if sys.hexversion >= 0x020700F0:
-            self.addCleanup(shutil.rmtree, self.tmp_path)
+        self.tmp_path = tempfile.mkdtemp(suffix=self.__class__.__name__)
+        self.addCleanup(shutil.rmtree, self.tmp_path)
         self.localedir = os.path.join(self.tmp_path, 'locale')
 
-    def tearDown(self):
-        if sys.hexversion < 0x020700F0:
-            shutil.rmtree(self.tmp_path)
-
     def test_00(self):
         # testing with default C locale, english
         lang = 'C'