Fix hostname rename feature

[Bischoff]

What does this PR change?

This PR fixes the test of hostname rename feature, where the cleanup was not working, and was making all subsequent feature tests fail.

It also adds idempotency, and a smoke test on the renamed server.

Links

Fixes: https://github.com/SUSE/spacewalk/issues/22323
Ports:

• 4.3: cannot port as the "refresh" parameter of get_target is not implemented yet:

# Get the Twopence node passing the host (includes lazy initialization)
def get_target(host)
  node = $node_by_host[host]
  node = twopence_init(host) if node.nil?
  node
end

To be clarified with Oscar.

Changelogs

• No changelog needed