vty_test_runner.py: fix socket leak

Each running test would open up another socket without ever closing unused
ones. Close the sockets after each test is done.

Change-Id: Ie433c8560de54f9a9d05fa07c44bae3126d19b30

openbsc/tests/vty_test_runner.py

@@ -57,6 +57,8 @@ class TestVTYBase(unittest.TestCase):
         self.vty = obscvty.VTYInteract(appstring, "127.0.0.1", appport)
 
     def tearDown(self):
+        if self.vty:
+            self.vty._close_socket()
         self.vty = None
         osmoutil.end_proc(self.proc)