Log when assassind detects the node is away

This information was not available in logs, assassind logs are now
availabe in UI.

Change-Id: Iae12dd28c82696c75226e7b60517316004cf69bd
Closes-Bug: #1307498

nailgun/nailgun/assassin/assassind.py

@@ -40,12 +40,15 @@ def update_nodes_status(timeout):
         datetime.now() > (Node.timestamp + timedelta(seconds=timeout))
     ).filter_by(online=True)
     for node_db in to_update:
+        away_message = u"Node '{0}' has gone away".format(
+            node_db.human_readable_name)
+
         notifier.notify(
             "error",
-            u"Node '{0}' has gone away".format(
-                node_db.human_readable_name),
+            away_message,
             node_id=node_db.id
         )
+        logger.warning(away_message)
     to_update.update({"online": False})
     db().commit()
 

nailgun/nailgun/settings.yaml

@@ -251,6 +251,11 @@ LOGS:
     <<: *local_log_type
     <<: *remote_syslog_log_format
     path: '/var/log/astute/astute.log'
+  - id: assassin
+    name: "Assassin"
+    <<: *local_log_type
+    <<: *python_log_format
+    path: '/var/log/nailgun/assassind.log'
   - id: ostf
     name: "HealthCheck"
     <<: *local_log_type