Move supervisor to it's own package

It allows to keep main namespace cleaner

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

supervisor/checkpoint.go

@@ -0,0 +1,25 @@
+package supervisor
+
+type CreateCheckpointEvent struct {
+	s *Supervisor
+}
+
+func (h *CreateCheckpointEvent) Handle(e *Event) error {
+	i, ok := h.s.containers[e.ID]
+	if !ok {
+		return ErrContainerNotFound
+	}
+	return i.container.Checkpoint(*e.Checkpoint)
+}
+
+type DeleteCheckpointEvent struct {
+	s *Supervisor
+}
+
+func (h *DeleteCheckpointEvent) Handle(e *Event) error {
+	i, ok := h.s.containers[e.ID]
+	if !ok {
+		return ErrContainerNotFound
+	}
+	return i.container.DeleteCheckpoint(e.Checkpoint.Name)
+}