lib: close stdin/out/err in non-terminal case

lib: close stdin/out/err in non-terminal case

Oops, forgot this path... in the --terminal case, stdio is closed when
the user ends the terminal session, but without terminal it was left
open.

(This caused a ssh session hang in the CentOS6 CI because the file
descriptors were still open, so ssh would keep the session alive...)

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>