Fixes SIGCHLD denials (why do we have it? we are userdebug!).
su shoud not run in init_shell, but this works for now.
The boss:
"Ok, given your usage model, I'd recommend just allowing it in your
policy.  But it doesn't make sense in our policy; that is not how we use
init_shell domain and we run su in the su domain (but that only exists
in userdebug or eng builds and therefore likely isn't suitable for your
usage)."