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)
By setting stdout to nil, won't we will loose all logging happening in nsenter before we exec the actual user command ?