Testnet: can't find peers, cant find blocks

**UPDATE:** I have destroyed my testnet node due to lack of interest. Community members who want to build a testnet should comment on this issue, or open a PR replacing the hsd testnet seed nodes, which are also inactive:

https://github.com/handshake-org/hsd/blob/fb6ce9fe4a884048e54654a591f0b002e829b81f/lib/protocol/networks.js#L585-L587

https://github.com/handshake-org/hsd/blob/fb6ce9fe4a884048e54654a591f0b002e829b81f/lib/net/seeds/testnet.js#L3-L8

~I have a testnet node up at:~

```
ai3shxm76z2fvdhv5rvbriloabhsghr6v43mi3zmtlq75ocbeb4wg@142.93.64.216
```

~You can connect like this:~

```
$ hsd --network=testnet \
--only=ai3shxm76z2fvdhv5rvbriloabhsghr6v43mi3zmtlq75ocbeb4wg@142.93.64.216
```

~I have `only` here to avoid bothering with the hard-coded testnet seeds which seem to be down. If you want to run a testnet node, add your IP in this discussion.~

Start with the testnet seed definitions in lib/protocol/networks.js and lib/net/seeds/testnet.js. Review how hsd selects testnet peers, then verify connectivity and block discovery with hsd --network=testnet using an active seed. Done means the referenced seed configuration points to working testnet nodes.

Written by the indexing model from the issue text.