* 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.
