Add the version string into the directory filename.

BUG=chromium:362570
TEST=None

Change-Id: I5f62d314def2ffb07ad8a436ea588356f4606dc1
Reviewed-on: https://chromium-review.googlesource.com/194286
Reviewed-by: David James <davidjames@chromium.org>
Tested-by: David James <davidjames@chromium.org>
diff --git a/lib/image_extractor.py b/lib/image_extractor.py
index 9349a1e..26de362 100644
--- a/lib/image_extractor.py
+++ b/lib/image_extractor.py
@@ -99,7 +99,8 @@
     """
     # Use the last 2 paths as the version_string path (may include board id).
     version_string = os.path.join(*image_dir.split(os.path.sep)[-2:])
-    cached_dir = os.path.join(image_dir, ImageExtractor.SRC_ARCHIVE_DIR)
+    cached_dir = os.path.join(image_dir, ImageExtractor.SRC_ARCHIVE_DIR,
+                              version_string)
     cached_image = os.path.abspath(os.path.join(
         cached_dir, self.image_to_extract))
     # If we previously unzipped the image, we're done.