Add initial system pkg to libcontainer

Port over console and ptmx code into console package
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)
Migrate selinux system xattr calls and prctl calls
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)
Finish removing the dependency on docker/pkg/system

Fixes #92
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)
Merge pull request #97 from crosbymichael/system-pkg

Remove the dep on dotcloud/docker/pkg/system