kubelet: move PodManager and MirrorClient to a subpackage

This change moves pod_manager.go and mirror_client.go to a separate package.
Also made necessary, minor changes to facilitate testing.

pkg/kubelet/runonce_test.go

@@ -26,14 +26,14 @@ import (
 	"k8s.io/kubernetes/pkg/kubelet/cadvisor"
 	kubecontainer "k8s.io/kubernetes/pkg/kubelet/container"
 	"k8s.io/kubernetes/pkg/kubelet/network"
+	kubepod "k8s.io/kubernetes/pkg/kubelet/pod"
 	"k8s.io/kubernetes/pkg/kubelet/status"
 )
 
 func TestRunOnce(t *testing.T) {
 	cadvisor := &cadvisor.Mock{}
 	cadvisor.On("MachineInfo").Return(&cadvisorApi.MachineInfo{}, nil)
-
-	podManager, _ := newFakePodManager()
+	podManager := kubepod.NewBasicPodManager(kubepod.NewFakeMirrorClient())
 	diskSpaceManager, _ := newDiskSpaceManager(cadvisor, DiskSpacePolicy{})
 	fakeRuntime := &kubecontainer.FakeRuntime{}