Stopped nodes are in diagnostic snapshot since now

Stopped nodes could be also helpful for troubleshooting, so including
them into the diagnostic snapshot.

Change-Id: Ib8608f8e04663d16249b514788522f701b9a88b9
Closes-Bug: #1599530

nailgun/nailgun/task/task.py

@@ -1857,7 +1857,8 @@ class DumpTask(object):
     def conf(cls):
         logger.debug("Preparing config for snapshot")
         nodes = db().query(Node).filter(
-            Node.status.in_(['ready', 'provisioned', 'deploying', 'error'])
+            Node.status.in_(['ready', 'provisioned', 'deploying',
+                             'error', 'stopped'])
         ).all()
 
         dump_conf = deepcopy(settings.DUMP)