Proposed fix for image content store

Signed-off-by: Daniel Nephin <dnephin@gmail.com>

image.go

@@ -32,6 +32,8 @@ type Image interface {
 	Config(ctx context.Context) (ocispec.Descriptor, error)
 	// IsUnpacked returns whether or not an image is unpacked.
 	IsUnpacked(context.Context, string) (bool, error)
+	// ContentStore provides a content store which contains image blob data
+	ContentStore() content.Store
 }
 
 var _ = (Image)(&image{})
@@ -166,3 +168,7 @@ func (i *image) getLayers(ctx context.Context, platform string) ([]rootfs.Layer,
 	}
 	return layers, nil
 }
+
+func (i *image) ContentStore() content.Store {
+	return i.client.ContentStore()
+}