Fix tarball sha1sum.

When a tarball is created for a tag, the branch-tip tarball is
not updated, but the sha1sum/md5sum commands were expecting
branch-tip tarballs.

Change-Id: I85c943ca93fae30237d458adae04c54d344c4c8f
Reviewed-on: https://review.openstack.org/19638
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins