Revert "Use b.pypi.python.org pypi mirror instead of pypi."

This reverts commit 1bac2431714b12fe6a2cd4adc830941710a722ff.

Turns out b.pypi.python.org is not a very complete mirror and ends up
creating new problems. Stop using it.

Change-Id: I640fad26cd8bd2546f73de460fd0dd944484d843
Reviewed-on: https://review.openstack.org/23321
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins