-[libguestfs] If qemu process is a shell script, then it is not cleaned
-up correctly, even on "good" exit. This is because we need to set up
-a new process group (see commented code for doing setpgid).
-[fixed? - added documentation in the manual page that you have to
-do 'exec qemu' in the wrapper. However I still notice that the
-recovery process kills qemu, instead of it being killed by the
-parent process, or at least that's what I think is happening]