rkt: Fix hostnetwork.

Mount hosts' /etc/hosts, /etc/resolv.conf, set host's hostname
when running the pod in the host's network.

Besides, do not set the DNS flags when running in host's network.

pkg/kubelet/container/helpers.go

@@ -179,3 +179,8 @@ func (irecorder *innerEventRecorder) PastEventf(object runtime.Object, timestamp
 		irecorder.recorder.PastEventf(ref, timestamp, eventtype, reason, messageFmt, args...)
 	}
 }
+
+// Pod must not be nil.
+func IsHostNetworkPod(pod *api.Pod) bool {
+	return pod.Spec.SecurityContext != nil && pod.Spec.SecurityContext.HostNetwork
+}