Add id to state command to return single container

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

supervisor/get_containers.go

@@ -5,6 +5,14 @@ type GetContainersEvent struct {
 }
 
 func (h *GetContainersEvent) Handle(e *Event) error {
+	if e.ID != "" {
+		ci := h.s.containers[e.ID]
+		if ci == nil {
+			return ErrContainerNotFound
+		}
+		e.Containers = append(e.Containers, ci.container)
+		return nil
+	}
 	for _, i := range h.s.containers {
 		e.Containers = append(e.Containers, i.container)
 	}