[v1.3.0, v1.3.1, v1.3.2] Gupax fails to start P2Pool due to unresolvable host IP
## OS & Version:
All OS's.

`v1.3.0`, `v1.3.1`, `v1.3.2`

## Bug
Gupax implemented a "backup hosts" feature for P2Pool in this commit: https://github.com/hinto-janai/gupax/commit/c4d534ec98e6c968feee74ffdfc7c980a2c3a165.

It was first released in `v1.3.0` and was enabled by default.

In `[Advanced]`, this will use the other user provided nodes as backup, however, in `[Simple]`, it will use _all_ other pre-packaged nodes in order of fastest to slowest.

`xmr.theuplink.net` (a node domain included in the affected versions) cannot be resolved by P2Pool:

```
2023-11-26 18:21:11.4910 Log started
2023-11-26 18:21:11.4919 P2Pool v3.5 (built with GCC/11.2.1 on Jun 30 2023)
2023-11-26 18:21:11.4920 Util UPnP: Started scanning for UPnP IGD devices
2023-11-26 18:21:11.6119 Util getaddrinfo failed for xmr.theuplink.net: Name does not resolve
2023-11-26 18:21:11.6119 P2Pool resolve_host failed for xmr.theuplink.net
2023-11-26 18:21:11.6158 Log stopped
```

This causes P2Pool to abort, causing Gupax to fail to start it, even though the other nodes in the list are okay.

## Steps
Steps to reproduce the behavior:
1. Enable `Backup host` toggle in `[P2Pool]` tab
2. Start `[P2Pool Simple]`
3. See error

## Temporary Workaround
Disable the `Backup host` toggle, and do not use `xmr.theuplink.net` as your node.

## Fix
- Assert nodes can be actually resolved and connected to
- Assert nodes can actually send/receive valid JSON-RPC requests before adding them onto the backup list 