cros flash: read latest link to resolve a revision

BUG=chromium:899801
TEST=precq

Change-Id: Ice26b19ff0b99aa1d4a8cdb1cf4987cc3d025f3f
Reviewed-on: https://chromium-review.googlesource.com/1308313
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Alex Klein <saklein@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/build_util.py b/build_util.py
index c421c87..daeca9b 100644
--- a/build_util.py
+++ b/build_util.py
@@ -32,8 +32,8 @@
 
     return os.path.realpath(src_root)
 
-  def GetLatestImageDir(self, board):
-    """Returns the latest image dir based on shell script."""
+  def GetLatestImageLink(self, board):
+    """Returns the latest image symlink."""
     return os.path.join(self.images_dir, board, 'latest')
 
   def GetDefaultBoardID(self):