Migrate to pbr.

Change-Id: I734f0f8237fb603ee41a39f06e63c007e79825a9
Reviewed-on: https://review.openstack.org/33350
Reviewed-by: James E. Blair <corvus@inaugust.com>
Reviewed-by: Doug Hellmann <doug.hellmann@dreamhost.com>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins