fix cluster-reachable unit (real test by creating a dummy resource)

Closes #2001 (closed)

This MR fixes the cluster-reachable unit (having it do a real "reachability test" by creating a dummy resource).

It also cleansup/simplifies the dummy unit_template which had some unused/not-needed parameters that !2911 (merged) could have removed but hadn't.

(Let's hope HAL will let us close #2001 (closed))