unittests: Fixes unit tests for Windows (part 2)

Currently, there are some unit tests that are failing on Windows due to
various reasons:

- volume mounting is a bit different on Windows: Mount will create the
  parent dirs and mklink at the volume path later (otherwise mklink will
  raise an error).
- os.Chmod is not working as intended on Windows.
- path.Dir() will always return "." on Windows, and filepath.Dir()
  should be used instead (which works correctly).
- on Windows, you can't typically run binaries without extensions. If
  the file C:\\foo.bat exists, we can still run C:\\foo because Windows
  will append one of the supported file extensions ($env:PATHEXT) to it
  and run it.
- Windows file permissions do not work the same way as the Linux ones.
- /tmp directory being used, which might not exist on Windows. Instead,
  the OS-specific Temp directory should be used.

Fixes a few other issues:

- rbd.go: Return error in a case in which an error is encountered. This
  will prevent "rbd: failed to setup" and "rbd: successfully setup" log
  messages to be logged at the same time.

pkg/volume/git_repo/git_repo_test.go

@@ -36,7 +36,7 @@ import (
 )
 
 func newTestHost(t *testing.T) (string, volume.VolumeHost) {
-	tempDir, err := ioutil.TempDir("/tmp", "git_repo_test.")
+	tempDir, err := ioutil.TempDir("", "git_repo_test.")
 	if err != nil {
 		t.Fatalf("can't make a temp rootdir: %v", err)
 	}
@@ -314,7 +314,7 @@ func doTestPlugin(scenario struct {
 	}
 
 	path := mounter.GetPath()
-	suffix := fmt.Sprintf("pods/poduid/volumes/kubernetes.io~git-repo/%v", scenario.vol.Name)
+	suffix := filepath.Join("pods/poduid/volumes/kubernetes.io~git-repo", scenario.vol.Name)
 	if !strings.HasSuffix(path, suffix) {
 		allErrs = append(allErrs,
 			fmt.Errorf("got unexpected path: %s", path))
@@ -439,7 +439,7 @@ func doTestSetUp(scenario struct {
 
 	var expectedPaths []string
 	for _, expected := range expecteds {
-		expectedPaths = append(expectedPaths, g.GetPath()+expected.dir)
+		expectedPaths = append(expectedPaths, filepath.Join(g.GetPath(), expected.dir))
 	}
 	if len(fcmd.Dirs) != len(expectedPaths) || !reflect.DeepEqual(expectedPaths, fcmd.Dirs) {
 		allErrs = append(allErrs,