Merge pull request #3210 from kubernetes-incubator/re-org-group_vars

inventory/sample/group_vars/all/all.yml

inventory/sample/group_vars/all/azure.yml

inventory/sample/group_vars/all/coreos.yml

inventory/sample/group_vars/all/docker.yml

inventory/sample/group_vars/all/oci.yml

inventory/sample/group_vars/all/openstack.yml

inventory/sample/group_vars/etcd.yml

inventory/sample/group_vars/k8s-cluster/addons.yml

inventory/sample/group_vars/k8s-cluster/k8s-cluster.yml

inventory/sample/hosts.ini