Change HTTP code: 404 to a more user friendly Image Not found msg

Docker-DCO-1.1-Signed-off-by: William Henry <whenry@redhat.com> (github: ipbabble)

Change the HTTP 4040 err msg. Need to reformat the go code for Travis.

Docker-DCO-1.1-Signed-off-by: William Henry <whenry@redhat.com> (github: ipbabble)

ran gofmt on this.

Docker-DCO-1.1-Signed-off-by: William Henry <whenry@redhat.com> (github: ipbabble)