ENH: adjust infoSwitch to report host subscription (related to #531)

• this compact form shows the subscription per host in the unsorted mpi order

  nProcs : 18
  Hosts  :
  (
      (node1 6)
      (node2 8)
      (node3 4)
  )

  This provides a succinct overview of which hosts have been subscribed or oversubscribed.

• The longer list of "slave.pid" ... remains available on the InfoSwitch 'writeHosts'