tests: cleanup test folder in teardown

Same as demo, tests expect a clean work directory, otherwise weird behavior will occur.

re6st/tests/test_end2end/test_registry_client.py

@@ -29,12 +29,12 @@ class TestRegistryClientInteract(unittest.TestCase):
 
     @classmethod
     def setUpClass(cls):
-        re6st_wrap.initial()
-
         # if running in net ns, set lo up
         subprocess.check_call(("ip", "link", "set", "lo", "up"))
 
     def setUp(self):
+        re6st_wrap.initial()
+
         self.port = 18080
         self.url = "http://localhost:{}/".format(self.port)
         # not important, used in network_config check

re6st/tests/test_network/re6st_wrap.py

@@ -29,8 +29,9 @@ RE6ST_CONF = PYTHON + " -m re6st.cli.conf"
 
 def initial():
     """create the workplace"""
-    if not WORK_DIR.exists():
-        WORK_DIR.mkdir()
+    if WORK_DIR.exists():
+        shutil.rmtree(str(WORK_DIR))
+    WORK_DIR.mkdir()
 
 def ip_to_serial(ip6):
     """convert ipv6 address to serial"""

re6st/tests/test_network/test_net.py

@@ -84,6 +84,8 @@ class TestNet(unittest.TestCase):
     def setUpClass(cls):
         """create work dir"""
         logging.basicConfig(level=logging.INFO)
+
+    def setUp(self):
         re6st_wrap.initial()
 
     @classmethod