The change in 818e82ecbbfc that caused to exit when the monitor

The change in 818e82ecbbfc that caused to exit when the monitor
dies created a race condition between the monitor exiting and the
status being read.  All we really want to do is make sure that
select() notifies us that there is a status change when the monitor
dies unexpectedly so shutdown the socketpair connected to the monitor
for writing when it dies.  That way we can still read the status
that is pending on the socket and select() on Linux will tell us
that the fd is ready.