Remove deprecated NOVA_RAX_AUTH

NOVA_RAX_AUTH has been deprecated in favor of a generic pluggable auth,
which in this case rackspace users can set OS_AUTH_SYSTEM=rackspace

Fixes bug 966329

Change-Id: Ie55fc36a0ac1cba61efa8bdd2f20809530d3365f
Merge "Remove deprecated NOVA_RAX_AUTH"