Propagation check exit aborts entire script and leaves stray DNS records

[sid3windr]

When the propagation check fails, the hook "exit" command fully exits dehydrated, causing stray DNS verification records to stay behind. This is pretty much fatal for the entire run and and subsequent ones, as the DNS output will never match correctly again.

[grischard]

Maybe something for an exit_hook. https://github.com/lukas2511/dehydrated/blob/master/docs/troubleshooting.md#dns-invalid-challenge-since-dehydrated-060--why-are-dns-challenges-deployed-first-and-verified-later is worth keeping in mind.