Have pip install the latest virtualenv.
Change-Id: Ifc5d32c36bf4231d1c0085e3e69ad879746bfb20
Reviewed-on: https://review.openstack.org/13804
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Monty Taylor <mordred@inaugust.com>
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Tested-by: Jenkins