Some power-by-mail hacking:

  - Bump the timeout for waiting for the operators to flip the switch
    to 20 minutes.

  - Fail fast if the node is in hwdown.  This case is intended to make
    an os_load fail for a robot-mounted mote whose robot is in hwdown.

  - Fail if the robotlab is not open since noone is around to do
    anything about it anyways.

  - Assume success if the event state for a node was updated
    "recently."  This is a fall back in case the powertime web page
    isn't used to notify the system that the node was powered
    on/cycled.  Also, do not send the SHUTDOWN event in this case.

  - Add a TBNodeEventStateUpdated() function to libdb.pm that returns
    true if the eventstate for a node was updated within N seconds
    from the current time.