SLIRP -smb support wants to fork a process and forget about reaping it.
To please it, add a generic service to register a process id and let
QEMU reap it. In the future it could be enhanced to pass a status,
but this would be unused.
With this in place, the SIGCHLD signal handler would not stomp on pclose
anymore.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
