RBD Plugin: Prepare to implement Attacher/Detacher interfaces.

1) Fix FakeMounter.IsLikelyNotMountPoint to return ErrNotExist if the
   directory does not exist. Mounter.IsLikelyNotMountPoint interface
   requires this, and RBD plugin depends on it.

pkg/util/mount/fake.go

@@ -17,6 +17,7 @@ limitations under the License.
 package mount
 
 import (
+	"os"
 	"path/filepath"
 	"sync"
 
@@ -136,6 +137,11 @@ func (f *FakeMounter) IsLikelyNotMountPoint(file string) (bool, error) {
 	f.mutex.Lock()
 	defer f.mutex.Unlock()
 
+	_, err := os.Stat(file)
+	if err != nil {
+		return true, err
+	}
+
 	// If file is a symlink, get its absolute path
 	absFile, err := filepath.EvalSymlinks(file)
 	if err != nil {

pkg/util/mount/safe_format_and_mount_test.go

@@ -18,6 +18,8 @@ package mount
 
 import (
 	"fmt"
+	"io/ioutil"
+	"os"
 	"runtime"
 	"testing"
 
@@ -50,6 +52,11 @@ func TestSafeFormatAndMount(t *testing.T) {
 	if runtime.GOOS == "darwin" || runtime.GOOS == "windows" {
 		t.Skipf("not supported on GOOS=%s", runtime.GOOS)
 	}
+	mntDir, err := ioutil.TempDir(os.TempDir(), "mount")
+	if err != nil {
+		t.Fatalf("failed to create tmp dir: %v", err)
+	}
+	defer os.RemoveAll(mntDir)
 	tests := []struct {
 		description   string
 		fstype        string
@@ -207,7 +214,7 @@ func TestSafeFormatAndMount(t *testing.T) {
 		}
 
 		device := "/dev/foo"
-		dest := "/mnt/bar"
+		dest := mntDir
 		err := mounter.FormatAndMount(device, dest, test.fstype, test.mountOptions)
 		if test.expectedError == nil {
 			if err != nil {