"verifypayloadmanifests" operation returns True if no manifest exists

[mistydemeo]

When run on a bag with no payload manifests, the "verifypayloadmanifests" operation returns true. This skipped test is indistinguishable from the result of "manifest checked, all files valid".

It would make sense for this to return an error - if "verify payload manifests" is explicitly requested, it seems strange to report success if there is no manifest to verify.