Add pypi mirror building slaves.

Change-Id: I9c5ea870d365f65ff19d91ca579ee127f67d9ea8
Reviewed-on: https://review.openstack.org/25314
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Monty Taylor <mordred@inaugust.com>
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Tested-by: Jenkins