Add a private method for nodepool server vars

A previous patch split the work done by get_openstack_vars into
costly and less-costly operations.  Nodepool only needs the
less-costly ones.  We will put that information in the shade API
in some form, but it has not been decided what form yet.  In the
mean time, allow Nodepool to easily call the method to perform
the less-costly operations for now.

Change-Id: I99bec7e4a709ef6b7623414dad5f1453070380f8

shade/__init__.py

@@ -1869,6 +1869,12 @@ class OpenStackCloud(object):
     def get_openstack_vars(self, server):
         return meta.get_hostvars_from_server(self, server)
 
+    def _expand_server_vars(self, server):
+        # Used by nodepool
+        # TODO(mordred) remove after these make it into what we
+        # actually want the API to be.
+        return meta.expand_server_vars(self, server)
+
     def available_floating_ip(self, network=None):
         """Get a floating IP from a network or a pool.