Allow HSDir retries more often in test networks
When a tor client tries all 6 (or, in small networks, 5) HSDirs, it won't try them again for 15 minutes. This is way too long for a network that bootstraps in 15 seconds.
Like we do with other timeout parameters, my branch (which I'm about to name after this ticket number) defines a _TESTING retry period, and uses it in test networks.