Merge \\"Skip copying existing vendor images\\" am: 1767d3f9

  # For devices using A/B update, copy over images from RADIO/ and/or

  # VENDOR_IMAGES/ to IMAGES/ and make sure we have all the needed

  # images ready under IMAGES/. All images should have '.img' as extension.

  banner("radio")

  ab_partitions = os.path.join(OPTIONS.input_tmp, "META", "ab_partitions.txt")

  if os.path.exists(ab_partitions):

    with open(ab_partitions, 'r') as f:

      lines = f.readlines()

    for line in lines:

      img_name = line.strip() + ".img"

      prebuilt_path = os.path.join(OPTIONS.input_tmp, "IMAGES", img_name)

      if os.path.exists(prebuilt_path):

        print "%s already exists, no need to overwrite..." % (img_name,)

        continue

      img_radio_path = os.path.join(OPTIONS.input_tmp, "RADIO", img_name)

      img_vendor_dir = os.path.join(

        OPTIONS.input_tmp, "VENDOR_IMAGES")