Put container's stdin behind TTY waitgroup.

[kobolog]

This fixes a race between runc run closing stdin on exit and TTY copier goroutine also trying to close it because of EOF on the console:

``` Read at 0x00c4200b8060 by main goroutine: os.(*file).close() /usr/local/go1.8/src/os/file_unix.go:136 +0xa4 os.(*File).Close() /usr/local/go1.8/src/os/file_unix.go:132 +0x55 main.(*tty).Close() go/src/github.com/opencontainers/runc/tty.go:120 +0x114 main.(*runner).run() go/src/github.com/opencontainers/runc/utils_linux.go:310 +0x966 main.startContainer() go/src/github.com/opencontainers/runc/utils_linux.go:395 +0x4ff main.glob..func13() go/src/github.com/opencontainers/runc/run.go:76 +0xe3 runtime.call32() /usr/local/go1.8/src/runtime/asm_amd64.s:514 +0x47 reflect.Value.Call() /usr/local/go1.8/src/reflect/value.go:302 +0xc0 github.com/urfave/cli.HandleAction() go/src/github.com/urfave/cli/app.go:487 +0x22d github.com/urfave/cli.Command.Run() go/src/github.com/urfave/cli/command.go:191 +0xdee github.com/urfave/cli.(*App).Run() go/src/github.com/urfave/cli/app.go:240 +0x8eb main.main() go/src/github.com/opencontainers/runc/main.go:138 +0x1249

Previous write at 0x00c4200b8060 by goroutine 9:
os.(*file).close()
/usr/local/go1.8/src/os/file_unix.go:143 +0x10a
os.(*File).Close()
/usr/local/go1.8/src/os/file_unix.go:132 +0x55
main.setupProcessPipes.func1()
go/src/github.com/opencontainers/runc/tty.go:57 +0xcc

Goroutine 9 (finished) created at:
main.setupProcessPipes()
go/src/github.com/opencontainers/runc/tty.go:58 +0x510
main.setupIO()
go/src/github.com/opencontainers/runc/utils_linux.go:163 +0x26e
main.(*runner).run()
go/src/github.com/opencontainers/runc/utils_linux.go:264 +0x6b5
main.startContainer()
go/src/github.com/opencontainers/runc/utils_linux.go:395 +0x4ff
main.glob..func13()
go/src/github.com/opencontainers/runc/run.go:76 +0xe3
runtime.call32()
/usr/local/go1.8/src/runtime/asm_amd64.s:514 +0x47
reflect.Value.Call()
/usr/local/go1.8/src/reflect/value.go:302 +0xc0
github.com/urfave/cli.HandleAction()
go/src/github.com/urfave/cli/app.go:487 +0x22d
github.com/urfave/cli.Command.Run()
go/src/github.com/urfave/cli/command.go:191 +0xdee
github.com/urfave/cli.(*App).Run()
go/src/github.com/urfave/cli/app.go:240 +0x8eb
main.main()
go/src/github.com/opencontainers/runc/main.go:138 +0x1249

</details>

[cyphar]

You need to add a Signed-off-by: line to your commit(s) which indicates that you attest the Developer Certificate of Origin a statement about your contributions that you must read before signing (don't worry, it's quite short and easy-to-read). You can add it to your commits with git commit --amend -s, and then doing a git push --force.