test__pool.py: avoid leaking greenlets out of the test case

--HG--
extra : transplant_source : %EEoaGe%7D%D3%D8fN%B4%7E%23%16%B7%0B%E0%11aI

greentest/test__pool.py

@@ -270,16 +270,18 @@ class TestJoinSleep(greentest.GenericWaitTestCase):
 
     def wait(self, timeout):
         p = pool.Pool()
-        p.spawn(gevent.sleep, 10)
+        g = p.spawn(gevent.sleep, 10)
         p.join(timeout=timeout)
+        g.kill()
 
 
 class TestJoinSleep_raise_error(greentest.GenericWaitTestCase):
 
     def wait(self, timeout):
         p = pool.Pool()
-        p.spawn(gevent.sleep, 10)
+        g = p.spawn(gevent.sleep, 10)
         p.join(timeout=timeout, raise_error=True)
+        g.kill()
 
 
 class TestJoinEmpty(greentest.TestCase):