Move logic around so that errors are caught in one place
Move logic around so that errors are caught in one place

Prevents a Docker::Error::NotFoundError being raised in what was the
container_image method.

openaustralia/morph,openaustralia/morph,openaustralia/morph,openaustralia/morph,openaustralia/morph,openaustralia/morph,openaustralia/morph