Remove terminal handling in libcontainer

Allocating the ptys are not needed inside the api right now.  The can be handled in the create method for a container.  We will have to add this in the new api when it's ready but for now I think we can push this to the caller above us and have them pass the stdin,out,and err that we need.  

Fixes #95

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)
Because this is interfaces :) Can be implemented by pointers and values. It'll not even compile with *, because `*io.Writer` not implementing `io.Writer` interface.