XBuddy path rewrites.

Set up default path rewrites.
Rewrites can be overridden by changing xbuddy_lookup_table.py

BUG=chromium:265917
TEST=manual
Attempt some of the default lookup paths defined in
xbuddy_lookup_table.py.
http://host:port/xbuddy/ --> serves latest local test image if it exists
http://host:port/xbuddy/ld --> serves latest local dev image if it exists
http://host:port/xbuddy/stable-update
http://host:port/xbuddy/paladin

Change-Id: I925ba37f3bfe6e61675aa35e0d89b837c8d5f0f3
Reviewed-on: https://gerrit.chromium.org/gerrit/63772
Commit-Queue: Joy Chen <joychen@chromium.org>
Reviewed-by: Joy Chen <joychen@chromium.org>
Tested-by: Joy Chen <joychen@chromium.org>
diff --git a/build_util.py b/build_util.py
index 0dfc97d..9bd4b24 100644
--- a/build_util.py
+++ b/build_util.py
@@ -32,3 +32,11 @@
     """Returns the latest image dir based on shell script."""
     cmd = '%s/get_latest_image.sh --board %s' % (self.scripts_dir, board)
     return os.popen(cmd).read().strip()
+
+  def GetDefaultBoardID(self):
+    """Returns the default board id stored in .default_board."""
+    board_file = '%s/.default_board' % (self.scripts_dir)
+    try:
+      return open(board_file).read()
+    except IOError:
+      return 'x86-generic'