Adds timeout and reincarnation test

Also found a bug because of this.

django_q/tests/test_cluster.py

@@ -1,6 +1,8 @@
 import sys
 import os
 from multiprocessing import Queue, Event, Value
+import threading
+from time import sleep
 
 import pytest
 
@@ -181,6 +183,20 @@ def test_async(r):
     assert result(h) == 12
     r.delete(list_key)
 
+@pytest.mark.django_db
+def test_timeout(r):
+    # set up the Sentinel
+    list_key = 'timeout_test:q'
+    async('django_q.tests.tasks.count_forever', list_key=list_key)
+    start_event = Event()
+    stop_event = Event()
+    # Set a timer to stop the Sentinel
+    threading.Timer(3, stop_event.set).start()
+    s = Sentinel(stop_event, start_event, list_key=list_key, timeout=1)
+    assert start_event.is_set()
+    assert s.status() == Conf.STOPPED
+    assert s.reincarnations == 1
+
 
 @pytest.mark.django_db
 def assert_result(task):