releasetools: Allow using futility-host to sign old TF.zip. am: 31a0de00

  elif info_dict.get("vboot", None):

    path = "/" + os.path.basename(sourcedir).lower()

    img_keyblock = tempfile.NamedTemporaryFile()

    cmd = [info_dict["vboot_signer_cmd"], info_dict["futility"],

    # We have switched from the prebuilt futility binary to using the tool

    # (futility-host) built from the source. Override the setting in the old

    # TF.zip.

    futility = info_dict["futility"]

    if futility.startswith("prebuilts/"):

      futility = "futility-host"

    cmd = [info_dict["vboot_signer_cmd"], futility,

           img_unsigned.name, info_dict["vboot_key"] + ".vbpubk",

           info_dict["vboot_key"] + ".vbprivk",

           info_dict["vboot_subkey"] + ".vbprivk",