Redirecting our output through outfilter.py is inherently a bit racy,
since the disk-image-create process will exit, and then you might get
outfilter.py flushing any remaining output as it closes.
On an interactive prompt this might lead to final output overwriting
the prompt, etc. This can be a bit confusing when you start running
things in a loop.
If we save the original fd, then on the exit path close the redirected
fd's and wait a little bit for final output (as a result of the
close), we get a more consistent output.
Change-Id: I8efe57ab421c1941e99bdecab62c6e21a87e4584
8fb2f5cb55