Image size include duplicate layers in the total size

[drudnev]

When running image size -n {image} you get total size of all layer in all tags . This counts each of the layers toward total size. Most images include base layers in each of the images thus do not need to be counted for each tag.

tag v1.0
layer: xyz
layer: abc

tag v1.1
layer: xyz
layer : cdf

Sum should be xyz + abc + cdf ( not xyz + abc + xyz + cdf )

I propose to pull out the sizeInfo to the outside loop and only count distinct layer to toward total image size.

		sizeInfo := make(map[string]int64)

		for _, tag := range tags {
			manifest, err := r.ImageManifest(imgName, tag)
			if err != nil {
				return cli.NewExitError(err.Error(), 1)
			}


			for _, layer := range manifest.Layers {
				sizeInfo[layer.Digest] = layer.Size
			}


		}

		for _, size := range sizeInfo {
			totalSize += size
		}
		fmt.Printf("%d %s\n", totalSize, imgName)