b=23961 fix for setup with several network interfaces

i=Brian.Murrell
i=Andrew.Perepechko

- metadata-updates fix for setup when several interfaces are UP on host;
  hostname could be assigned to IP which is different from lnet network used,
  the hostname-s of NODES_TO_USE are now stored in HOSTS
- new SHUTDOWN_ATTEMPTS: the tunable number of attepts to shutdown node
- shutdown_node_hard () fix: do not call "power off" each time,
  wait that the node is not pingable before the next "power off" attempt
- unused check_port() is removed