Add API endpoint for overcloud Keystone

The logic of querying the overcloud entrypoints are specific to the
TripleO/Tuskar Heat templates. This API endpoint provides a way for the client
to be independent of this logic.

Change-Id: I552d007d4e1bd3a7558d16138ef96a23a25394ea
Implements: blueprint tuskar-api-return-endpoints

docs/api/curl.rst

@@ -10,6 +10,7 @@ Resources
 -  `ResourceClass <#resource_class>`_
 -  `DataCenter <#data_center>`_
 -  `Node <#node>`_
+-  `Overcloud <#overcloud>`_
 
 Rack
 ----
@@ -418,4 +419,29 @@ response
             }
     }
 
+Overcloud
+----------
+
+get Keystone URL for an overcloud
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+    curl -X GET -H 'Content-Type:application/json' -H 'Accept: application/json' http://0.0.0.0:8585/v1/overclouds/cloudname
+
+response
+^^^^^^^^
+
+::
+
+    {
+        "stack_name": "cloudname",
+        "links": [
+            {
+                "rel": "keystone",
+                "href": "http://192.0.2.5:5000/v2.0/"
+            }
+        ]
+    }
+
 `back to top <#index>`_