Comment 1 for bug 1592281

Although it isn't really clear to me what to do with devices that claim to have no chassis at all, it seems we need to fix this problem in two ways:

First, the 'missing devices' algorithm should handle the case where a missing device is unknown to any plugins - but this will result in deleting it during a statuscheck.

Second, the system plugin should probably never create the chassis device in the first place, if it sees that the device has no chassis but at least one root entity.