Added health_check thread cancelling in BlockingPool

Author: vladvildanov

redis/connection.py

@@ -1669,3 +1669,11 @@ def disconnect(self):
         self._checkpid()
         for connection in self._connections:
             connection.disconnect()
+
+        # Send an event to stop scheduled healthcheck execution.
+        if self._hc_cancel_event is not None and not self._hc_cancel_event.is_set():
+            self._hc_cancel_event.set()
+
+        # Joins healthcheck thread on disconnect.
+        if self._hc_thread is not None and not self._hc_thread.is_alive():
+            self._hc_thread.join()