Handle edge case where all node(s) may be unavailable.

[dtzxporter]

We're using this in a scenario where we resolve the endpoints from a dns entry. It would be nice to be able to have something like this baked into the library, so that in the event all nodes become unavailable, the library can recover by querying the dns entry again.

[dtzxporter]

A method to set/remove nodes would also help, because then we can implement this externally.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.