Move supervisor to it's own package

It allows to keep main namespace cleaner

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

supervisor/update.go

@@ -0,0 +1,41 @@
+package supervisor
+
+import "github.com/docker/containerd/runtime"
+
+type UpdateEvent struct {
+	s *Supervisor
+}
+
+func (h *UpdateEvent) Handle(e *Event) error {
+	i, ok := h.s.containers[e.ID]
+	if !ok {
+		return ErrContainerNotFound
+	}
+	container := i.container
+	if e.State.Status != "" {
+		switch e.State.Status {
+		case runtime.Running:
+			if err := container.Resume(); err != nil {
+				return ErrUnknownContainerStatus
+			}
+		case runtime.Paused:
+			if err := container.Pause(); err != nil {
+				return ErrUnknownContainerStatus
+			}
+		default:
+			return ErrUnknownContainerStatus
+		}
+	}
+	if e.Signal != nil {
+		// signal the pid1/main process of the container
+		processes, err := container.Processes()
+		if err != nil {
+			return err
+		}
+		if len(processes) == 0 {
+			return ErrProcessNotFound
+		}
+		return processes[0].Signal(e.Signal)
+	}
+	return nil
+}