Automatic merge from submit-queue (batch tested with PRs 50087, 39587, 50042, 50241, 49914)

plugin/pkg/client/auth: add openstack auth provider

This is an implementation of auth provider for OpenStack world, just like python-openstackclient, we read the environment variables of a list `OS_*`, and client will cache a token to interact with each components, we can do the same here, the client side can cache a token locally at the first time, and rotate automatically when it expires.

This requires an implementation of token authenticator at server side, refer:

1.  [made by me] https://github.com/kubernetes/kubernetes/pull/25536, I can carry this on when it is fine to go.
2.  [made by @kfox1111] https://github.com/kubernetes/kubernetes/pull/25391

The reason why I want to add this is due to the `client-side` nature, it will be confusing to implement it downstream, we would like to add this support here, and customers can get `kubectl` like they usually do(`brew install kubernetes-cli`), and it will just work.

When this is done, we can deprecate the password keystone authenticator as the following reasons:

1.  as mentioned at some other places, the `domain` is another parameters which should be provided.
2.  in case the user supplies `apikey` and `secrets`, we might want to fill the `UserInfo` with the real name which is not implemented for now.

cc @erictune @liggitt 

```
add openstack auth provider
```