Fix download link in aws/kubecfg documentation

Kubecfg's download link on Darwin and Linux are points to http://storage.googleapis.com/k8s/darwin/kubecfg .
Later one should be changed to http://storage.googleapis.com/k8s/linux/kubecfg .
Cleanups of ipv6 changes.

I was late re-reviewing and some comments did not get resolved.
Merge pull request #2417 from thockin/ipalloc

Cleanups of ipv6 changes.
Merge branch 'eparis-rename-to-kube'

* eparis-rename-to-kube:
  rename kube server binaries to kube-
Merge pull request #2414 from hodduc/fix-aws-doc

Fix download link in aws/kubecfg documentation