Fixes EndpointNotFound after deployment

After deploying an overcloud via the UI, the generic error page for
Horizon is displayed.  With debugging enabled, an EndpointNotFound
error message is displayed.  This is caused by the dashboard_urls
method attempting to access a method on the overcloud keystone client
before the overcloud keystone service is initialized.

This patch wraps the code to check for initialized services in a
try block and returns an empty list in the event an exception is
thrown.

Change-Id: I7da53ea085b2728950c3a0c2760d0745119e6ff1
Resolves: rhbz#1245192

tuskar_ui/api/heat.py

@@ -429,12 +429,14 @@ class Stack(base.APIResourceWrapper):
         if not client:
             return []
 
-        services = client.services.list()
-
-        for service in services:
-            if service.name == 'horizon':
-                break
-        else:
+        try:
+            services = client.services.list()
+            for service in services:
+                if service.name == 'horizon':
+                    break
+            else:
+                return []
+        except Exception:
             return []
 
         admin_urls = [endpoint.adminurl for endpoint