Add a private method for nodepool server vars
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

openstack-infra/shade,dtroyer/python-openstacksdk,dtroyer/python-openstacksdk,stackforge/python-openstacksdk,openstack/python-openstacksdk,openstack-infra/shade,openstack/python-openstacksdk,stackforge/python-openstacksdk