Failing to remove an image, will not remove the image name/tag.

Fixes #7845 and #7801, and a real pain point I had :)

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)
should it just be an if on it's own line? it's making sure that it failed with the right error