Comment 1 for bug 1195057

Note that we only need to check the image master, image signing, and device signing keyrings. The blacklist keyring is *always* downloaded anew (and thus its signature is always checked). The archive master is *never* downloaded - it must exist on the file system and it is presumed to be valid. If the archive master were corrupt we couldn't do anything about it anyway, except exit with an error that the user probably couldn't (easily) recover from.