recvtty: fix waiting for both goroutines
recvtty: fix waiting for both goroutines

It looks like we need to wait for the both copy goroutines to finish,
not just the one that happen to finish first.

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

dqminh/runc,rhatdan/runc,xiaochenshen/runc,opencontainers/runc,estesp/runc,rhatdan/runc,xiaochenshen/runc,opencontainers/runc,kolyshkin/runc,kolyshkin/runc,opencontainers/runc,kolyshkin/runc,dqminh/runc,estesp/runc,rhatdan/runc,rhatdan/runc,dqminh/runc,opencontainers/runc,dqminh/runc,kolyshkin/runc,estesp/runc,xiaochenshen/runc