Fix: cts: properly clean up after remote node testing

Previously, when cleaning up after remote a node test, CTS would clear CLI
constraints for the dummy resource only for the remote node being tested,
and it would remove the remote node connection resource from the CIB, but not
the remote node itself.

However, the CLI might have added negative constraint(s) for cluster node(s) as
well, causing resource deletion to fail later. Failing to remove the remote node
cluttered status output and could affect later tests.

Now, CTS clears dummy resource CLI constraints for all nodes, and removes
the remote node.