Added keystone host to os-apply-config

Tuskar isn't yet using puppet for its configuration, but it needs to be
configured to authenticate its APIs [1]. That change needs access to the
keystone host.

Instead of just looking up local-ip, I followed the conventions used
for configuring Ironic's auth which used keystone.host as the key.

[1] https://review.openstack.org/#/c/185117/

Change-Id: I5f78813ccea01a60fc50fef18d28b29438671bc8

elements/undercloud-stack-config/config.json.template

@@ -39,6 +39,9 @@
     }
    ]
   },
+  "keystone": {
+    "host": "{{LOCAL_IP}}"
+  },
   "ironic": {
     "service-password": "{{UNDERCLOUD_IRONIC_PASSWORD}}"
   },