statemachine: not receiving commands blocks Stopping and http endpoint

[schmichael]

If a stateful task handler does not receive on its command chan, the Stop() method can block indefinitely which in turn can block things like the httputil info handler which check the stopped flag of every running task.

Since all of these paths must acquire the lock around the tasks stop flag, they all block and make it hard if not impossible to tell what task is causing the issue!