Fix etcd client generation (#10769)

* ci: redefine multinode to node-etcd-client

This should allow to catch several class of problem rather than just
one -> from network plugin such as calico or cilium talking directly to
the etcd.

* Dynamically define etcd host range

This has two benefits:
- We don't play the etcd role twice for no reason
- We have access to the whole cluster (if needed) to use things like
  group_by.

tests/cloud_playbooks/roles/packet-ci/vars/main.yml

@@ -7,7 +7,7 @@ _vm_count_dict:
   ha-recover: 3
   ha-recover-noquorum: 3
   all-in-one: 1
-  multinode: 3
+  node-etcd-client: 4
   default: 2
 
 vm_count: "{{ _vm_count_dict[mode | d('default')] }}"