Fix duplication of nodes in NodeName

[jovial]

Prior to this change slurmctld would fail to start if adding nodes to multiple partitions e.g:

openhpc_slurm_partitions:
    - name: allnodes
      groups:
        - name: alfa
        - name: beta
      partition_params:
        Priority: 50
      default: YES
    - name: alfa
      partition_params:
        Priority: 100
    - name: bravo
      partition_params:
        Priority: 100

This change tracks all nodes that already have a NodeName entry and will not add again.

[jovial]

This does not require using filters outside of the role like the workaround we have previously used:

# As per the docs:
# - A partition entry may contain groups. If it doesn't the partition itself is the group.
# - Nodes can only be in one group (else slurmctld startup fails with "fatal: Duplicated NodeName"
#   due to the templating approach. Howver $group.partition_params.Nodes can be used to
#   override the automatic definition of Node=.
# - To avoid having to explicitly list the nodes, we can use the hostlist_expression
#   filter provided by the stackhpc.openhpc role. This works as this expression is
#   evaluated inside the role. NB: this filter returns a list.
# - Have to handle the GPU nodes not existing in staging.
_general_nodes:
  - "{{ groups[openhpc_cluster_name + '_general'] | hostlist_expression | join(',') }}"
  - "{{ groups.get(openhpc_cluster_name + '_a40_1024', []) | hostlist_expression | join(',') }}"
  - "{{ groups.get(openhpc_cluster_name + '_a40_512', []) | hostlist_expression | join(',') }}"

openhpc_slurm_partitions:
  - name: general # all nodes except grid - this templates the actual ${cluster_name}-general nodes ...
    partition_params:
      Nodes: "{{ _general_nodes | join(',') }}" # .. this adds the other nodes
    default: YES
  - name: gpu # all GPU nodes
    groups:
      - name: a40_1024
        gres:
          - conf: gpu:A40:2
            file: /dev/nvidia[0-1]
      - name: a40_512
        gres:
          - conf: gpu:A40:2
            file: /dev/nvidia[0-1]
    default: NO

[sjpb]

Can someone add a molecule test for this specific case please?

[sjpb]

Can we get a) a molecule test and b) docs changes to match up with code behaviour changes please.