docs: def get_clusters_interfaces(clusters, extra_cond=lambda nic: True):
      """ Returns for each cluster the available cluster interfaces
  
      Args:
          clusters (str): list of the clusters
          extra_cond (lambda): extra predicate to filter network card retrieved
      from the API. E.g lambda nic: not nic['mounted'] will retrieve all the
      usable network cards that are not mounted by default.
  
      Returns:
          dict of cluster with their associated nic names
  
      Examples:
          .. code-block:: python
  
              # pseudo code
              actual = get_clusters_interfaces(["paravance"])
              expected = {"paravance": ["eth0", "eth1"]}
              assertDictEquals(expected, actual)
      """
  
      interfaces = {}
      for cluster in clusters:
          nics = get_cluster_interfaces(cluster, extra_cond=extra_cond)
          interfaces.setdefault(cluster, nics)
  
      return interfaces