Add kubelet DNS flags & api disable for DNS

This adds --cluster_dns and --cluster_domain flags to kubelet.  If
non-empty, kubelet will set docker --dns and --dns-search flags based on
these.  It uses the cluster DNS and appends the hosts's DNS servers.
Likewise for DNS search domains.

This also adds API support to bypass cluster DNS entirely, needed to
bootstrap DNS.

cmd/kubelet/kubelet.go

@@ -63,12 +63,15 @@ var (
 	cAdvisorPort            = flag.Uint("cadvisor_port", 4194, "The port of the localhost cAdvisor endpoint")
 	oomScoreAdj             = flag.Int("oom_score_adj", -900, "The oom_score_adj value for kubelet process. Values must be within the range [-1000, 1000]")
 	apiServerList           util.StringList
+	clusterDomain           = flag.String("cluster_domain", "", "Domain for this cluster.  If set, kubelet will configure all containers to search this domain in addition to the host's search domains")
+	clusterDNS              = util.IP(nil)
 )
 
 func init() {
 	flag.Var(&etcdServerList, "etcd_servers", "List of etcd servers to watch (http://ip:port), comma separated. Mutually exclusive with -etcd_config")
 	flag.Var(&address, "address", "The IP address for the info server to serve on (set to 0.0.0.0 for all interfaces)")
 	flag.Var(&apiServerList, "api_servers", "List of Kubernetes API servers to publish events to. (ip:port), comma separated.")
+	flag.Var(&clusterDNS, "cluster_dns", "IP address for a cluster DNS server.  If set, kubelet will configure all containers to use this for DNS resolution in addition to the host's DNS servers")
 }
 
 func setupRunOnce() {
@@ -114,6 +117,8 @@ func main() {
 		RegistryBurst:           *registryBurst,
 		MinimumGCAge:            *minimumGCAge,
 		MaxContainerCount:       *maxContainerCount,
+		ClusterDomain:           *clusterDomain,
+		ClusterDNS:              clusterDNS,
 		Runonce:                 *runonce,
 		Port:                    *port,
 		CAdvisorPort:            *cAdvisorPort,