chutney verify hangs on tor hs data transmission verification

chutney hs verify hangs under the latest tor 0.2.7-alpha-dev. Verification of clients, exits, bridges and IPv6 bridges works fine.

hs verify worked in 01d988d72f9eae798a36d1c8bb226b9e8f4fe3f1 (after teor/bug-15642-v3-fallback-unit-tests was merged), but now hangs in 63a90f2df4dcd7fff862ca3849f3aa3b1dec7e84.

This may be due to:

• dgoulet's changes in #14845 (moved) or #14847 (moved),
• andrea's changes in #14840 (moved),
• nickm's changes in #15546 (moved), or
• cypherpunks' changes in #15344 (moved) which were merged in between those commits.

It worries me that we may have broken hidden services, so I have listed this as "critical".

I'll look into this when I get time in the next day or two, but I wanted to log the bug so everyone knew about it.