Use WoT TD Directory TD as a test case

[mmccool]

The WoT Discovery spec defines a TD (example) for a TD Directory (TDD) and this is (a) a good test case for a sophisticated TD (b) something that node-wot should talk to "internally" as part of discovery.

Suggest at least using the TD as a test case by trying to consume it with node-wot.
See w3c/wot-testing#71

Note also that we MAY want to use a TM for directories in the discovery spec itself (if the definition of TM is expanded to meet our needs).