docs: def update_cluster(cluster_ref, cluster_spec):
      '''
      Updates a cluster in a datacenter.
  
      cluster_ref
          The cluster reference.
  
      cluster_spec
          The cluster spec (vim.ClusterConfigSpecEx).
          Defaults to None.
      '''
      cluster_name = get_managed_object_name(cluster_ref)
      log.trace('Updating cluster \'%s\'', cluster_name)
      try:
          task = cluster_ref.ReconfigureComputeResource_Task(cluster_spec,
                                                             modify=True)
      except vim.fault.NoPermission as exc:
          log.exception(exc)
          raise salt.exceptions.VMwareApiError(
              'Not enough permissions. Required privilege: '
              '{}'.format(exc.privilegeId))
      except vim.fault.VimFault as exc:
          log.exception(exc)
          raise salt.exceptions.VMwareApiError(exc.msg)
      except vmodl.RuntimeFault as exc:
          log.exception(exc)
          raise salt.exceptions.VMwareRuntimeError(exc.msg)
      wait_for_task(task, cluster_name, 'ClusterUpdateTask')