Put some actual hsdescs in the unit tests for parsing

Right now our test_rend_fns() function in src/test/test.c builds a "rend_service_descriptor_t *generated", and then it encodes it, and then it parses it, to make sure it gets the expected descriptor back. That's a great start.

But there are now several different versions of the descriptor format in play, and our unit tests by definition only test the one that the current Tor version generates.

Also, it would be easier to play around with "how Tor handles it if you take that stanza out of the descriptor" experiments, if there are some actual descriptors in the unit tests.

Good idea / bad idea?