Merge "Allow data wipe for full OTAs"

    # We should only allow downgrading incrementals (as opposed to full).

    # Otherwise the device may go back from arbitrary build with this full

    # OTA package.

    if OPTIONS.incremental_source is None:

  if OPTIONS.incremental_source is None and OPTIONS.downgrade:

    raise ValueError("Cannot generate downgradable full OTAs")

  # TODO(xunchang) for retrofit and partial updates, maybe we should rebuild the