Changed GetAllZones to only get zones with nodes that are currently

running (renamed to GetAllCurrentZones). Added E2E test to confirm this
behavior.

Added node informer to cloud-provider controller to keep track of zones
with k8s nodes in them.

pkg/cloudprovider/cloud.go

@@ -23,6 +23,7 @@ import (
 
 	"k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/client-go/informers"
 	"k8s.io/kubernetes/pkg/controller"
 )
 
@@ -49,6 +50,11 @@ type Interface interface {
 	HasClusterID() bool
 }
 
+type InformerUser interface {
+	// SetInformers sets the informer on the cloud object.
+	SetInformers(informerFactory informers.SharedInformerFactory)
+}
+
 // Clusters is an abstract, pluggable interface for clusters of containers.
 type Clusters interface {
 	// ListClusters lists the names of the available clusters.