MAINT: disable rackspace uploads

[tylerjereddy]

• the community has apparently lost free services
  with rackspace hosting: https://mail.python.org/pipermail/scipy-dev/2020-February/023990.html

• as a first step torward migration, and to prevent undesired
  charges, disable rackspace uploads of our OpenBLAS build
  artifacts from CI

cc @matthew-brett @mattip @ogrisel

I beleive @aterrel noted that there was an extenion, but Olivier has no confirmation for the specific container we are using, and Andy wanted the migration to happen sooner than later anyway given recent events.

Once disabled, we can start to experiment with alternative solutions.

[tylerjereddy]

Also note that the multibuild submodule has:

GF_LIB_URL="https://3f23b170c54c2533c070-1c8a9b3114517dc5fe17b7c3f8c63a43.ssl.cf2.rackcdn.com"

Presumably can be overriden if we do re-enable auto-uploads somewhere else.

[charris]

@mattip I'm wondering if now might be a good time to move numpy-wheels to the numpy repo.

[aterrel]

If you want to move on to NumFOCUS' rackspace account let me know and we can figure out how to arrange it.

…

[tylerjereddy]

cc @rgommers @pv thoughts or preferences? I think appveyor stores the built tarballs for a while so they could be manually downloaded/released in a GitHub release when needed. I can't remember if Travis CI does that for us at the moment.

[mattip]

I'm wondering if now might be a good time to move numpy-wheels to the numpy repo.

@charris Probably @matthew-brett would have a better formed opinion about the cost-benefits. If we no longer upload to rackspace, the move would be easier.

[mattip]

LGTM. s390x is failing with write /var/lib/docker/tmp/GetImageBlob529035649: no space left on device, not connected to this PR.