Merge "build_image: Query the actual image size after invoking the final mkfs." am: 0096a750

  if not mkfs_output:

    mkfs_output = BuildImageMkfs(in_dir, prop_dict, out_file, target_out, fs_config)

  # Update the image (eg filesystem size). This can be different eg if mkfs

  # rounds the requested size down due to alignment.

  prop_dict["image_size"] = common.sparse_img.GetImagePartitionSize(out_file)

  # Check if there's enough headroom space available for ext4 image.

  if "partition_headroom" in prop_dict and fs_type.startswith("ext4"):

    CheckHeadroom(mkfs_output, prop_dict)