Add support for following redirects to the SpdyRoundTripper. This is
necessary for clients using it directly (e.g. the apiserver talking
directly to the kubelet) because the CRI streaming server issues a
redirect for streaming requests.
Also extract common logic for following redirects.
Kubernetes-commit: 715d5d9c91c669cf33c0bf9a9c9d352c6c4228a6