open_init_pty: restore stdin/stdout to blocking upon exit

At exit, restore stdin and stdout to blocking.

Test: run_init id && run_init id
Test: open_init_pty bash -c 'echo hello; exec >&- 2>&- <&-; sleep 1;'

Fixes: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=863187
Fixes: https://bugs.gentoo.org/show_bug.cgi?id=621062
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
1 file changed