Remove empty downloaded_* directories

These are created automatically when their contents is actually
downloaded during testing, so there is no need to keep empty directories
in git. By removing them it is possible to share the same directories
between multiple git working trees, by simply making symlinks (which was
not possible before without ending up with a modified working tree).

Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>

Author: matthijskooijman

src/arduino.cc/builder/test/.gitignore

@@ -0,0 +1 @@
+downloaded_*

src/arduino.cc/builder/test/downloaded_board_manager_stuff/.gitignore

@@ -139,6 +139,8 @@ func DownloadCoresAndToolsAndLibraries(t *testing.T) {
 }
 
 func patchFiles(t *testing.T) {
+	err := utils.EnsureFolderExists(PATCHES_FOLDER)
+	NoError(t, err)
 	files, err := ioutil.ReadDir(PATCHES_FOLDER)
 	NoError(t, err)