stop extending thread

it's just too difficult to get right when also intending to keep a
reference to an event that must be consulted from the parent - opt
insteda to create an objectthat quacks much like a Thread but creates
one internally at a time of its pleasing

tests/support/serversupp.py

@@ -26,10 +26,10 @@
 
 """Configuration related details within the test support library."""
 
-import threading
+from threading import Thread, Event as ThreadEvent
 
 
-class ServerWithinThreadExecutor(threading.Thread):
+class ServerWithinThreadExecutor:
     """Execute a server within a thread ensuring we are able to
     block until it is ready to recieve test requests.
 
@@ -38,10 +38,10 @@ class ServerWithinThreadExecutor(threading.Thread):
     the server is ready to handle requests."""
 
     def __init__(self, ServerClass, *args, **kwargs):
-        super(ServerWithinThreadExecutor, self).__init__()
         self._serverclass = ServerClass
         self._arguments = (args, kwargs)
-        self._started = threading.Event()
+        self._started = ThreadEvent()
+        self._thread = None
         self._wrapped = None
 
     def run(self):
@@ -56,15 +56,20 @@ def run(self):
         except Exception as e:
             pass
 
+    def start(self):
+        self._thread = Thread(target=self.run)
+        self._thread.start()
+
     def start_wait_until_ready(self):
         self.start()
-        if not self._started.is_set():
-            self._started.wait()
+        self._started.wait()
         return self
 
     def stop(self):
         self.stop_server()
-        self.join()
+        self._wrapped = None
+        self._thread.join()
+        self._thread = None
 
     def stop_server(self):
         self._wrapped.shutdown()