Merge "build_image.py: Make sparse squashfs images"

  elif fs_type.startswith("squash"):

    build_command = ["mksquashfsimage.sh"]

    build_command.extend([in_dir, out_file])

    build_command.extend(["-s"])

    build_command.extend(["-m", prop_dict["mount_point"]])

    if "selinux_fc" in prop_dict:

      build_command.extend(["-c", prop_dict["selinux_fc"]])