Change default for [notifications]/default_publisher_id to $host

The default used in code for CONF.notifications.default_publisher_id
is CONF.host, which is a free-form StrOpt.

In an upcoming change, the "my_ip" option is going to be changed from
a StrOpt to an IPOpt, so we made the default value change for
the default_publisher_id option before that.

Change-Id: Ia85130f66bd5a60097e8967064559fd0962d06fd
Closes-Bug: #1713150

nova/conf/notifications.py

@@ -65,7 +65,7 @@ API service.
 
     cfg.StrOpt(
         'default_publisher_id',
-        default='$my_ip',
+        default='$host',
         deprecated_group='DEFAULT',
         deprecated_for_removal=True,
         deprecated_since='17.0.0',
@@ -81,12 +81,12 @@ notifications using different publisher, change this value accordingly.
 
 Possible values:
 
-* Defaults to the IPv4 address of this host, but it can be any valid
+* Defaults to the current hostname of this host, but it can be any valid
   oslo.messaging publisher_id
 
 Related options:
 
-*  my_ip - IP address of this host
+*  host - Hostname, FQDN or IP address of this host.
 """),
     cfg.StrOpt(
         'notification_format',

nova/tests/unit/test_notifications.py

@@ -19,6 +19,7 @@ import copy
 import datetime
 
 import mock
+from oslo_config import cfg
 from oslo_context import context as o_context
 from oslo_context import fixture as o_fixture
 from oslo_utils import timeutils
@@ -36,6 +37,8 @@ from nova.tests.unit import fake_network
 from nova.tests.unit import fake_notifier
 from nova.tests import uuidsentinel as uuids
 
+CONF = cfg.CONF
+
 
 class NotificationsTestCase(test.TestCase):
 
@@ -625,6 +628,7 @@ class NotificationsTestCase(test.TestCase):
         self.assertEqual(n.event_type, func_name)
         self.assertEqual(n.context, ctxt)
         self.assertTrue(self.decorated_function_called)
+        self.assertEqual(CONF.host, n.publisher_id)
 
 
 class NotificationsFormatTestCase(test.NoDBTestCase):

releasenotes/notes/bug-1713150-default_publisher_id-f46f4f6a39347951.yaml

@@ -0,0 +1,5 @@
+---
+upgrade:
+  - |
+    The ``[notifications]/default_publisher_id`` configuration option now
+    defaults to ``[DEFAULT]/host`` rather than ``[DEFAULT]/my_ip``.