Merge pull request #36095 from caesarxuchao/deprecate-LegacyHostIP

Automatic merge from submit-queue

[RFC] Prepare for deprecating NodeLegacyHostIP

Ref https://github.com/kubernetes/kubernetes/issues/9267#issuecomment-257994766

*What this PR does*
- Add comments saying "LegacyHostIP" will be deprecated in 1.7;
- Add v1.NodeLegacyHostIP to be consistent with the internal API (useful for client-go migration #35159)
- Let cloudproviders who used to only set LegacyHostIP set the IP as both InternalIP and ExternalIP
- Master used to ssh tunnel to node's ExternalIP or LegacyHostIP to do [healthz check](https://github.com/kubernetes/kubernetes/blame/master/pkg/master/master.go#L328-L332). OTOH, if on-prem, kubelet only [sets](https://github.com/kubernetes/kubernetes/blob/master/pkg/kubelet/kubelet_node_status.go#L430-L431) LegacyHostIP or InternalIP. In order to deprecate LegacyHostIP in 1.7, I let healthz check to use InternalIP if ExternalIP is not available. (The healthz check is the only consumer of LegacyHostIP in k8s.)

@liggitt @justinsb @bgrant0607 

```release-note
LegacyHostIP will be deprecated in 1.7.
```

pkg/api/types.go

@@ -2598,6 +2598,7 @@ type NodeAddressType string
 // These are valid address types of node. NodeLegacyHostIP is used to transit
 // from out-dated HostIP field to NodeAddress.
 const (
+	// Deprecated: NodeLegacyHostIP will be removed in 1.7.
 	NodeLegacyHostIP NodeAddressType = "LegacyHostIP"
 	NodeHostName     NodeAddressType = "Hostname"
 	NodeExternalIP   NodeAddressType = "ExternalIP"