The usecase of this change:
When a super user grant some RBAC permissions to a group, he can use
--as-group to test whether the group get the permissions.
Note that now we support as-groups, as-user-extra in kubeconfig file
after this change.
Kubernetes-commit: e541defd49d01024d17dddf8e966eba2c46a6db0
Change validateClusterInfo to use clientcmdapi.NewCluster() instead of
clientcmdapi.Cluster{} when comparing against the passed in clusterInfo.
clusterInfo most likely will be a combination of
clientcmdapi.NewCluster() merged with potential overrides. This is
necessary because otherwise, the DeepEqual between what is supposed to
be an empty Cluster and clusterInfo will fail, resulting in an error
that doesn't allow fall-through to checking for in-cluster
configuration.
Kubernetes-commit: 266ba9ffdeeeeba8022ce94ae4e725d996c29363
