Web UI (topology graph): Show FQDN for nodes if they have no common DNS zone
It allows to avoid confusion with identical short hostnames.
There are two cases implemented:
- no common DNS zone: graph shows FQDN for all nodes
- all nodes have one common DNS zone: graph shows DN relatively to the common zone
https://pagure.io/freeipa/issue/7206
Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>