[Nut-upsuser] stale/dead ups logic

[d tbsky]

hi:
    when testing nut in our environment, we found something that nut
maybe tune for "stale/dead ups" situation. currently the "dead ups"
are assume alive(eg: host shutdown unnecessary), unless it is in the
"OB" state before going to stale.

   our environment (ServerA + ServerB forms a cluster):

  ServerA-> usb to UPSA -> two PS power by  UPSA and UPSB -> upsmon
monitor two UPS
  ServerB-> usb to UPSB -> two PS power by UPSA and UPSB -> upsmon
monitor two UPS

now if ServerB crash and then power's been cut,  ServerA won't
shutdown since UPSB is stale/dead.

in  Server A situation, I want to assume UPSA is "alive/no need
shutdown" when it is stale, but I want to assume UPSB is "dead/need
shutdown" when it is stale. to accomplish that, maybe uspmon can have
a flag to indicate that:

 MONITOR ftups at localhost 1 monmaster passmaster master alive
 MONITOR ftups at 10.1.1.1 1 monslave nutslave slave dead

 maybe there are other situations that people want to declare "stale"
ups as "dead/need shutdown"..

Regards,
tbskyd