a node has failed.

* In the main wait loop, I check the eventstate for the node, for
  TBFAILED or PXEFAILED. Neither of these should happen after the
  reboot, so it makes sense to quit waiting if they do.

* I added an event handler to libosload, specifically to watch for
  nodes entering RELOADSETUP or RELOADING, after the reboot. Because
  of the race with reboot, this was best done with a handler instead
  of polling the DB state like case #1 above. The idea is that a node
  should hit one of these two states within a fairly short time (I
  currently have it set to 5 minutes). If not, something is wrong and
  the loop bails on that node. ÊWhat happens after is subject to the
  normal waiting times.

I believe that these two tests will catch a lot of cases where osload
is waiting on something that will never finish.