Revise node sorting

We are using a new schema for sorting nodes. This patch replaces the
'sort_keys' and the 'sort_dir' parameters with a single 'sort'
parameter.

Change-Id: I72ea5dfc4b9d63b2f558e2b0b7992d167bc27a8e

senlin/api/openstack/v1/nodes.py

@@ -83,8 +83,7 @@ class NodeController(object):
             'cluster_id': 'single',
             'limit': 'single',
             'marker': 'single',
-            'sort_dir': 'single',
-            'sort_keys': 'multi',
+            'sort': 'single',
             'global_project': 'single',
         }
         params = util.get_allowed_params(req.params, param_whitelist)