Fix support for forward slashes in cd_files for Windows (#115)

Packer recommends that we use "/" as the path separator. There is a
problem with using it on Windows because of the following behaviour:

We might pass paths with forward slashes in `StepCreateCD` struct

The string `rootFolder, err := tmp.Dir("packer_to_cdrom")` makes
rootFolder use system-based slashes, which is "\" for Windows.

This rootFolder is passed to `s.AddFile(rootFolder, toAdd)`

And a mix of two slashes ruins our replace logic while going through
the `visit` function. We end up having different slashes for `allDirs`
and `discardPath` in
`intermediaryDirs := strings.Replace(allDirs, discardPath, "", 1)`

We change our replace login to don't depend on slashes.

The tests we had didn't cover such cases as we passed all files with
paths constructed with filepath.Join(dir, fname) which returns paths
with "\\" on Windows. So we added a test case to specifically check
forward slashes.

multistep/commonsteps/step_create_cdrom.go

@@ -260,7 +260,9 @@ func (s *StepCreateCD) AddFile(dst, src string) error {
 		// Clean up pathing so that we preserve the base directory provided by
 		// the user but not the local pathing to that directory.
 		allDirs, base := filepath.Split(pathname)
-		intermediaryDirs := strings.Replace(allDirs, discardPath, "", 1)
+		allDirsSlashSafe := filepath.ToSlash(allDirs)
+		discardPathSlashSafe := filepath.ToSlash(discardPath)
+		intermediaryDirs := strings.Replace(allDirsSlashSafe, discardPathSlashSafe, "", 1)
 
 		dstPath := filepath.Join(dst, base)
 		if intermediaryDirs != "" {

multistep/commonsteps/step_create_cdrom_test.go

@@ -93,28 +93,33 @@ func TestStepCreateCD(t *testing.T) {
 	defer os.RemoveAll(dir)
 
 	createFiles(t, dir, map[string]string{
-		"test folder/b/test1": "1",
-		"test folder/b/test2": "2",
-		"test folder 2/x":     "3",
-		"test_cd_roms.tmp":    "4",
-		"test cd files.tmp":   "5",
-		"Test-Test-Test5.tmp": "6",
-		"subfolder/meta-data": "subfolder/meta-data from files",
-		"subfolder/user-data": "subfolder/user-data from files",
-		"user-data":           "user-data from files",
-		"vendor-data":         "vendor-data from files",
+		"test folder/b/test1":    "1",
+		"test folder/b/test2":    "2",
+		"test folder 2/x":        "3",
+		"test_cd_roms.tmp":       "4",
+		"test cd files.tmp":      "5",
+		"Test-Test-Test5.tmp":    "6",
+		"fwdslashes/nested/test": "7",
+		"subfolder/meta-data":    "subfolder/meta-data from files",
+		"subfolder/user-data":    "subfolder/user-data from files",
+		"user-data":              "user-data from files",
+		"vendor-data":            "vendor-data from files",
 	})
 	step.Content = map[string]string{
 		"subfolder not created by files/test.tmp": "test",
 		"subfolder/meta-data":                     "subfolder/meta-data from content",
 		"user-data":                               "user-data from content",
 	}
 
-	files := []string{"test folder", "test folder 2/", "test_cd_roms.tmp", "test cd files.tmp", "Test-Test-Test5.tmp", "subfolder", "user-data", "vendor-data"}
+	files := []string{"test folder", "test folder 2/", "test_cd_roms.tmp", "test cd files.tmp", "Test-Test-Test5.tmp", "fwdslashes", "subfolder", "user-data", "vendor-data"}
 
 	step.Files = make([]string, len(files))
 	for i, fname := range files {
-		step.Files[i] = filepath.Join(dir, fname)
+		fullPath := filepath.Join(dir, fname)
+		if fname == "fwdslashes" {
+			fullPath = filepath.ToSlash(fullPath)
+		}
+		step.Files[i] = fullPath
 	}
 	action := step.Run(context.Background(), state)
 
@@ -139,6 +144,7 @@ func TestStepCreateCD(t *testing.T) {
 		"test_cd_roms.tmp":                        "4",
 		"test cd files.tmp":                       "5",
 		"Test-Test-Test5.tmp":                     "6",
+		"fwdslashes/nested/test":                  "7",
 		"subfolder not created by files/test.tmp": "test",
 		"subfolder/meta-data":                     "subfolder/meta-data from content",
 		"subfolder/user-data":                     "subfolder/user-data from files",