start breaking up controller manager into two pieces

Addresses: kubernetes/enhancements#88

This commit starts breaking the controller manager into two pieces, namely,

1. cloudprovider dependent piece
2. coudprovider agnostic piece

the controller manager has the following control loops -

 - nodeController
 - volumeController
 - routeController
 - serviceController
 - replicationController
 - endpointController
 - resourcequotacontroller
 - namespacecontroller
 - deploymentController etc..

among the above controller loops,

 - nodeController
 - volumeController
 - routeController
 - serviceController

are cloud provider dependent. As kubernetes has evolved tremendously, it has become difficult
for different cloudproviders (currently 8), to make changes and iterate quickly. Moreover, the
cloudproviders are constrained by the kubernetes build/release lifecycle. This commit is the first
step in moving towards a kubernetes code base where cloud providers specific code will move out of
the core repository, and will be maintained by the cloud providers themselves.

I have added a new cloud provider called "external", which signals the controller-manager that
cloud provider specific loops are being run by another controller. I have added these changes in such
a way that the existing cloud providers are not affected. This change is completely backwards compatible, and
does not require any changes to the way kubernetes is run today.

Finally, along with the controller-manager, the kubelet also has cloud-provider specific code, and that will
be addressed in a different commit/issue.

cmd/kube-controller-manager/app/controllermanager.go

@@ -290,17 +290,20 @@ func StartControllers(s *options.CMServer, kubeconfig *restclient.Config, rootCl
 	if err != nil {
 		glog.Warningf("Unsuccessful parsing of service CIDR %v: %v", s.ServiceCIDR, err)
 	}
-	nodeController, err := nodecontroller.NewNodeController(
-		sharedInformers.Pods(), sharedInformers.Nodes(), sharedInformers.DaemonSets(),
-		cloud, client("node-controller"),
-		s.PodEvictionTimeout.Duration, s.NodeEvictionRate, s.SecondaryNodeEvictionRate, s.LargeClusterSizeThreshold, s.UnhealthyZoneThreshold, s.NodeMonitorGracePeriod.Duration,
-		s.NodeStartupGracePeriod.Duration, s.NodeMonitorPeriod.Duration, clusterCIDR, serviceCIDR,
-		int(s.NodeCIDRMaskSize), s.AllocateNodeCIDRs)
-	if err != nil {
-		glog.Fatalf("Failed to initialize nodecontroller: %v", err)
+
+	if s.CloudProvider != "external" {
+		nodeController, err := nodecontroller.NewNodeController(
+			sharedInformers.Pods(), sharedInformers.Nodes(), sharedInformers.DaemonSets(),
+			cloud, client("node-controller"),
+			s.PodEvictionTimeout.Duration, s.NodeEvictionRate, s.SecondaryNodeEvictionRate, s.LargeClusterSizeThreshold, s.UnhealthyZoneThreshold, s.NodeMonitorGracePeriod.Duration,
+			s.NodeStartupGracePeriod.Duration, s.NodeMonitorPeriod.Duration, clusterCIDR, serviceCIDR,
+			int(s.NodeCIDRMaskSize), s.AllocateNodeCIDRs)
+		if err != nil {
+			glog.Fatalf("Failed to initialize nodecontroller: %v", err)
+		}
+		nodeController.Run()
+		time.Sleep(wait.Jitter(s.ControllerStartInterval.Duration, ControllerStartJitter))
 	}
-	nodeController.Run()
-	time.Sleep(wait.Jitter(s.ControllerStartInterval.Duration, ControllerStartJitter))
 
 	serviceController, err := servicecontroller.New(cloud, client("service-controller"), s.ClusterName)
 	if err != nil {

pkg/cloudprovider/plugins.go

@@ -90,8 +90,12 @@ func InitCloudProvider(name string, configFilePath string) (Interface, error) {
 	var cloud Interface
 	var err error
 
-	if name == "" {
-		glog.Info("No cloud provider specified.")
+	if name == "" || name == "external" {
+		outputCloud := name
+		if outputCloud == "" {
+			outputCloud = "No"
+		}
+		glog.Infof("%s cloud provider specified.", outputCloud)
 		return nil, nil
 	}