Fix short UUID support

[perigrin]

We either need to properly support short UUIDs everywhere (if possible) or stop claiming we do. Or preferably the latter until the former happens.

Short UUIDs are the first segment of the UUID (e.g. 7fcae66f) and were previously allowed in places like the Data Center lookup.

[perigrin]

We removed mention of short UUIDs in 7aa5d3a but I'm leaving this ticket open to remind me that we could try to actually support them (again).