Modify nodes to register directly with the master.

- Delete nodes when they are no longer ready and don't exist in the
cloud provider.
 - Label each node with it's hostname.
 - Add flag to skip node registration.
 - Add a test for registering an existing node.

pkg/cloudprovider/cloud.go

@@ -17,6 +17,7 @@ limitations under the License.
 package cloudprovider
 
 import (
+	"errors"
 	"net"
 	"strings"
 
@@ -86,6 +87,8 @@ type Instances interface {
 	Release(name string) error
 }
 
+var InstanceNotFound = errors.New("instance not found")
+
 // Zone represents the location of a particular machine.
 type Zone struct {
 	FailureDomain string