DNS Check - Make dynamic based on Team subnet

[resetcentral]

DNS checks currently use a static IP for each record. We should make it dynamic based on the team's subnet.

[mcutshaw]

Isn't this no longer an issue?

[resetcentral]

Still an issue. Current workaround just checks the last octet which would be the same for each team.

DNS checker here.

Ideally expected['answer'] would be unique to each team (or a template string we could fill with a team id).