testThreadTaskWaitWhenNotStarted failure

Investigate and fix the following test. It's working but Python interpreter is hanging at the end (thread not joined?).

``` python
    def testThreadTaskWaitWhenNotStarted(self):
        """test task_wait() when workers not started"""

        for i in range(1, 5):
            task = Task()
            task.shell("sleep %d" % i)

        task_wait()
        task.resume()
```
