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'