When running under nodepool in a foreground, non-daemonized situation
without a tty (i.e. within a container) we're seeing this "wait" hang
indefinitely.
It is probably related to "outfilter.py" and output file descriptors,
although TBH we haven't completely root-caused it. I won't claim this
is a great solution, but it should hopefully let the dib process
finish and just die, where outfilter will disappear.
Change-Id: If78da54df3d4c240fee16aee4413ec554b37c1d6
bee30b43d2