Fix doc for service list

If a service is enabled, the "disabled_reason" field in response
for /v2/.{tenant_id}./os-services/detail is null, however, currently
it's specified as "" in the doc, thus may be confusing to users.

This patch change the template and doc, it should not cause issue to
existing applications.

Change-Id: Ia71ec4c97a355bcc1a7b63e6107db77f80a5d843
Close-bug: 1328382

doc/api_samples/os-services/services-get-resp.json

@@ -25,7 +25,7 @@
             "status": "enabled",
             "updated_at": "2012-09-19T06:55:34.000000",
             "zone": "internal",
-            "disabled_reason": ""
+            "disabled_reason": null
         },
         {
             "binary": "nova-compute",

doc/api_samples/os-services/services-get-resp.xml

@@ -1,6 +1,6 @@
 <services>
     <service status="disabled" binary="nova-scheduler" zone="internal" state="up" host="host1" updated_at="2012-10-29 13:42:02" disabled_reason="test1"/>
     <service status="disabled" binary="nova-compute" zone="nova" state="up" host="host1" updated_at="2012-10-29 13:42:05" disabled_reason="test2"/>
-    <service status="enabled" binary="nova-scheduler" zone="internal" state="down" host="host2" updated_at="2012-09-19 06:55:34" disabled_reason=""/>
+    <service status="enabled" binary="nova-scheduler" zone="internal" state="down" host="host2" updated_at="2012-09-19 06:55:34" disabled_reason="None"/>
     <service status="disabled" binary="nova-compute" zone="nova" state="down" host="host2" updated_at="2012-09-18 08:03:38" disabled_reason="test4"/>
 </services>

doc/v3/api_samples/os-services/services-list-get-resp.json

@@ -23,7 +23,7 @@
         {
             "id": 3,
             "binary": "nova-scheduler",
-            "disabled_reason": "",
+            "disabled_reason": null,
             "host": "host2",
             "state": "down",
             "status": "enabled",

nova/tests/api/openstack/compute/contrib/test_services.py

@@ -61,7 +61,7 @@ fake_services_list = [
          topic='scheduler',
          updated_at=datetime.datetime(2012, 9, 19, 6, 55, 34),
          created_at=datetime.datetime(2012, 9, 18, 2, 46, 28),
-         disabled_reason=''),
+         disabled_reason=None),
     dict(test_service.fake_service,
          binary='nova-compute',
          host='host2',
@@ -278,7 +278,7 @@ class ServicesTest(test.TestCase):
                      'status': 'enabled',
                      'state': 'down',
                      'updated_at': datetime.datetime(2012, 9, 19, 6, 55, 34),
-                     'disabled_reason': ''},
+                     'disabled_reason': None},
                     {'binary': 'nova-compute',
                      'host': 'host2',
                      'zone': 'nova',

nova/tests/api/openstack/compute/plugins/v3/test_services.py

@@ -59,7 +59,7 @@ fake_services_list = [
          topic='scheduler',
          updated_at=datetime.datetime(2012, 9, 19, 6, 55, 34),
          created_at=datetime.datetime(2012, 9, 18, 2, 46, 28),
-         disabled_reason=''),
+         disabled_reason=None),
     dict(test_service.fake_service,
          binary='nova-compute',
          host='host2',
@@ -194,7 +194,7 @@ class ServicesTest(test.TestCase):
                      'status': 'enabled',
                      'state': 'down',
                      'updated_at': datetime.datetime(2012, 9, 19, 6, 55, 34),
-                     'disabled_reason': ''},
+                     'disabled_reason': None},
                     {'binary': 'nova-compute',
                      'host': 'host2',
                      'id': 4,
@@ -437,7 +437,7 @@ class ServicesCellsTest(test.TestCase):
                      'state': 'down',
                      'updated_at': datetime.datetime(2012, 9, 19, 6, 55, 34,
                                                      tzinfo=utc),
-                     'disabled_reason': ''},
+                     'disabled_reason': None},
                     {'id': 'cell1@4',
                      'binary': 'nova-compute',
                      'host': 'host2',

nova/tests/integrated/api_samples/os-services/services-get-resp.json.tpl

@@ -21,7 +21,7 @@
         {
             "binary": "nova-scheduler",
             "host": "host2",
-            "disabled_reason": "",
+            "disabled_reason": null,
             "state": "down",
             "status": "enabled",
             "updated_at": "%(strtime)s",

nova/tests/integrated/api_samples/os-services/services-get-resp.xml.tpl

@@ -2,6 +2,6 @@
 <services>
   <service status="disabled" binary="nova-scheduler" zone="internal" state="up" updated_at="%(xmltime)s" host="host1" disabled_reason="test1"/>
   <service status="disabled" binary="nova-compute" zone="nova" state="up" updated_at="%(xmltime)s" host="host1" disabled_reason="test2"/>
-  <service status="enabled" binary="nova-scheduler" zone="internal" state="down" updated_at="%(xmltime)s" host="host2" disabled_reason=""/>
+  <service status="enabled" binary="nova-scheduler" zone="internal" state="down" updated_at="%(xmltime)s" host="host2" disabled_reason="None"/>
   <service status="disabled" binary="nova-compute" zone="nova" state="down" updated_at="%(xmltime)s" host="host2" disabled_reason="test4"/>
 </services>

nova/tests/integrated/v3/api_samples/os-services/services-list-get-resp.json.tpl

@@ -22,7 +22,7 @@
         },
         {
             "binary": "nova-scheduler",
-            "disabled_reason": "",
+            "disabled_reason": null,
             "host": "host2",
             "id": 3,
             "state": "down",