don't propagate ImageID in MapContainerImage2Name
don't propagate ImageID in MapContainerImage2Name

This was building a set of all the image ids represented by the same
unversioned image. Well, it was doing that until I broke it with a
silly mistake in #1739 - instead of extracting the imageID from the
original node ID, it's extracting it from the updated ID, which is the
unversioned image. Even if it was working though, it's pointless
since nothing is looking at that info.

weaveworks/scope,weaveworks/scope,kinvolk/scope,kinvolk/scope,alban/scope,kinvolk/scope,alban/scope,kinvolk/scope,kinvolk/scope,alban/scope,alban/scope,weaveworks/scope,weaveworks/scope,alban/scope,weaveworks/scope,alban/scope,kinvolk/scope,weaveworks/scope