[CI] Ensure that the devnet always uses IPv4

[kaimast]

The following changes are part of #4039. However, they are independent of the proposed block sync changes, so a separate PR will make reviewing easier.

Recently, I ran into an in issue where nodes resolve localhost of a peer address to [::1] instead of 127.0.0.1. In the future, we may want to try both addresses, but it is fine to just force IPv4 for CI/testing.
To do this, this PR ensures 127.0.0.1 is passed instead of localhost throughout the script.

Additionally, this PR changes the trusted peers setup slightly. The old version created an array $trusted_peers but then treated it as a string when trimming the trailing comma and when passing it to the validator in --peers "$trusted_peers". The proposed change always treats trusted_peers as a simple string.
I noticed this error, when some clients did not sync and shellcheck helped with debugging. In the future, it would e great if we ran shellcheck or another linter on the bash script in CI.

Finally, the PR also prints clients log on failure, which was helpful in the specific problem I had above.