local.NewImage fails because docker.SaveImage returns multiple manifests.

[ekcasey]

Periodically when executing the lifecycle against the daemon errors like this occur:

ERROR: rebase working image: manifest.json had unexpected number of entries: 2

This happens when we are saving an image from the docker daemon to disk and we unexpectedly get more than one manifest.

imgutil/local/local.go

Lines 542 to 544 in afd98bd

	if len(manifest) != 1 {
	return nil, fmt.Errorf("manifest.json had unexpected number of entries: %d", len(manifest))
	}

We should figure out how we get into this state and determine a mitigation.