This is a small configuration struct used in two scenarios:
1. To attach I/O pipes to a running containers.
2. To attach to execution processes inside running containers.
Although they are similar, keeping the struct in the same package
than exec and container can generate cycled dependencies if we
move any of them outside the daemon, like we want to do
with the container.
Signed-off-by: David Calavera <david.calavera@gmail.com>
