don't re-use a TempDir path

Rather than creating and immediately removing a temp directory to get a
random path name, fetch files into a subdirectory.

config/module/get.go

@@ -3,6 +3,7 @@ package module
 import (
 	"io/ioutil"
 	"os"
+	"path/filepath"
 
 	"github.com/hashicorp/go-getter"
 )
@@ -37,13 +38,10 @@ func GetCopy(dst, src string) error {
 	if err != nil {
 		return err
 	}
-	// FIXME: This isn't completely safe. Creating and removing our temp path
-	//        exposes where to race to inject files.
-	if err := os.RemoveAll(tmpDir); err != nil {
-		return err
-	}
 	defer os.RemoveAll(tmpDir)
 
+	tmpDir = filepath.Join(tmpDir, "module")
+
 	// Get to that temporary dir
 	if err := getter.Get(tmpDir, src); err != nil {
 		return err