spaced ignores SIGINT in RPC retry loop

### How to reproduce

1. Start local `bitcoind`
2. Start `spaced`
3. Stop `bitcoind`

You will end with the infinite retry loop
```
ERROR spaced::source] Rpc: Transport: error sending request for url (http://127.0.0.1:18443/) - retrying in 100ms...
```

Ctr+C is ignored by `spaced` in this state.