Add Load for container and Task with Attach

This adds both container and task loading of running tasks as well as
reattaching to the IO of the task after load.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

task.go

@@ -33,6 +33,7 @@ type Task interface {
 	Exec(context.Context, *specs.Process, IOCreation) (Process, error)
 	Processes(context.Context) ([]uint32, error)
 	CloseStdin(context.Context) error
+	IO() *IO
 }
 
 type Process interface {
@@ -168,3 +169,7 @@ func (t *task) CloseStdin(ctx context.Context) error {
 	})
 	return err
 }
+
+func (t *task) IO() *IO {
+	return t.io
+}