Create and use keystone_admin[project|user]

It is not always convenient to use the the given
admin project and admin user; especially when some clouds
use different user and project for there keystone 'admin'

This allows setting the variables for these users to something
else, and defaults them to there current values of 'admin'.

Change-Id: I22b79a30f01c90a92ecc0974886edf3791518f2f