Add domain_id to /v3 group responses

The example responses for the identity /v3 group responses
(create, get, and update group) didn't include the domain_id like
the real response does.

Change-Id: I8f8c20f0862a326e1496e037ef545acf31042d3f

api-ref/src/wadls/identity-api/src/v3/samples/GroupCreateResponse.json

@@ -1,6 +1,7 @@
 {
     "group": {
         "description": "Developers cleared for work on secret projects",
+        "domain_id": "--domain-id--",
         "id": "--group-id--",
         "links": {
             "self": "http://identity:35357/v3/groups/--group-id--"

api-ref/src/wadls/identity-api/src/v3/samples/GroupGetResponse.json

@@ -1,6 +1,7 @@
 {
     "group": {
         "description": "Developers cleared for work on secret projects",
+        "domain_id": "--domain-id--",
         "id": "--group-id--",
         "links": {
             "self": "http://identity:35357/v3/groups/--group-id--"

api-ref/src/wadls/identity-api/src/v3/samples/GroupUpdateResponse.json

@@ -1,6 +1,7 @@
 {
     "group": {
         "description": "Developers cleared for work on secret projects",
+        "domain_id": "--domain-id--",
         "id": "--group-id--",
         "links": {
             "self": "http://identity:35357/v3/groups/--group-id--"