Don't accept tasks for stopped managers

In case a provider manager is being replaced due to a configuration
change, raise exceptions for any tasks submitted after it is stopped.

This will probably cause many errors, but they should already be
handled and servers will eventually be deleted.

We can minimize the disruption by making the provider managers more
adaptable to changes, but this stopgap measure should at least fix
the current problem we are observing with threads that get stuck
and never complete.

Change-Id: I3d190881ede30480d7c4ae970a0cb2dd07c3e160

nodepool/provider_manager.py

@@ -276,10 +276,6 @@ class ProviderManager(TaskManager):
             return True
         return False
 
-    def submitTask(self, task):
-        self.queue.put(task)
-        return task.wait()
-
     def findFlavor(self, min_ram, name_filter=None):
         # Note: this will throw an error if the provider is offline
         # but all the callers are in threads (they call in via CreateServer) so

nodepool/task_manager.py

@@ -86,5 +86,7 @@ class TaskManager(threading.Thread):
             self.queue.task_done()
 
     def submitTask(self, task):
+        if not self._running:
+            raise Exception("Manager %s is no longer running" % self.name)
         self.queue.put(task)
         return task.wait()