Change cloud provider CreateTCPLoadBalancer to return endpoint as string

Some load balancers (particularly AWS ELB) define the public endpoint
as a hostname (instead of using IP addresses).

This is a partial fix for #5224; there will also be some proxy work.

pkg/api/types.go

@@ -720,6 +720,9 @@ type ServiceSpec struct {
 	CreateExternalLoadBalancer bool `json:"createExternalLoadBalancer,omitempty"`
 	// PublicIPs are used by external load balancers, or can be set by
 	// users to handle external traffic that arrives at a node.
+	// For load balancers, the publicIP will usually be the IP address of the load balancer,
+	// but some load balancers (notably AWS ELB) use a hostname instead of an IP address.
+	// For hostnames, the user will use a CNAME record (instead of using an A record with the IP)
 	PublicIPs []string `json:"publicIPs,omitempty"`
 
 	// ContainerPort is the name or number of the port on the container to direct traffic to.