Some fixes to node add and re-add

The patch changes the pre-checks in node-add and re-add:
  - if the node is not already in the cluster, refuse to re-add
  - when re-adding, reuse the secondary IP from the cluster
    configuration
  - when re-adding, reset the offline and drained flags, so that RPC
    calls work (and we can actually upload the keys)

The patch also adds a missing log entry in LUSetNodeParams.

Reviewed-by: imsnah