libct: close execFifo after start
libct: close execFifo after start

Apparently, the parent never closes execFifo fd. Not a problem for runc
per se, but can be an issue for a user of libcontainer.

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

kolyshkin/runc,rhatdan/runc,dqminh/runc,dqminh/runc,opencontainers/runc,dqminh/runc,rhatdan/runc,kolyshkin/runc,opencontainers/runc,opencontainers/runc,rhatdan/runc,kolyshkin/runc,rhatdan/runc,opencontainers/runc,dqminh/runc,kolyshkin/runc