Slirp uses fork_exec for spawning service processes, and QEMU uses this
for running smbd. As SIGCHLD is not handled, these processes become
zombies on termination. Fix this by installing a proper signal handler,
but also make sure we disable the signal while waiting on forked network
setup/shutdown scripts.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com> Signed-off-by: Mark McLoughlin <markmc@redhat.com>