Disable label rewrite if shortenLabelsFlag is false (#359)

shortenLabelsFlas is being used in edit ShortenLabels function
but not used in rewrite ShortenLabels, which causes all the labels to be
shorten though this flag it is set to false.

buildozer/BUILD.bazel

@@ -6,6 +6,7 @@ go_library(
     importpath = "github.com/bazelbuild/buildtools/buildozer",
     visibility = ["//visibility:private"],
     deps = [
+        "//build:go_default_library",
         "//edit:go_default_library",
         "//tables:go_default_library",
     ],

buildozer/main.go

@@ -20,6 +20,7 @@ import (
 	"os"
 	"strings"
 
+	"github.com/bazelbuild/buildtools/build"
 	"github.com/bazelbuild/buildtools/edit"
 	"github.com/bazelbuild/buildtools/tables"
 )
@@ -75,6 +76,9 @@ func main() {
 		}
 	}
 
+	if !(*shortenLabelsFlag) {
+		build.DisableRewrites = []string{"label"}
+	}
 	edit.ShortenLabelsFlag = *shortenLabelsFlag
 	edit.DeleteWithComments = *deleteWithComments
 	opts := &edit.Options{