fix goroutines leak and exit code

two issues:
* `docker run ubuntu rtyuioyu` fails with and ugly message, after when do you `docker ps -l` you don't see any status of exit code
* `docker run ubuntu rtyuioyu` leaks a goroutine (can you check with `docker info -D`)

This PR depends on https://github.com/docker/libcontainer/pull/132
I think we can just take these changes from here and fix the go routine leak right?