AbstractCacheManager destroy Framework's executorService when shutdown

The executorService in AbstractCacheManager is passed in from outside and belongs to FrameworkModel. However, when an ApplicationModel is destroyed, the destroy of AbstractCacheManager will be triggered, and the public executorService will be shut down, causing other ApplicationModels to no longer be able to refresh the dubbo cache.

---

AbstractCacheManager中的executorService是外部传入，属于FrameworkModel，但是一个ApplicationModel销毁时，会触发AbstractCacheManager的destroy，就把这个公共的executorService shutdown 了，导致其他ApplicationModel不能再刷新dubbo cache