ResourceManager onEvict cause segmentation fault with AnnoyModelFetcher

Current implementation causes the segmentation fault when the query on edges that bind to custom EdgeFetcher, more specifically AnnoyModelFetcher with cacheTTLInSecs as -1.

cacheTTLInSecs -1 means we initialize EdgeFetcher instance instead of using local cached instance.

SafeUpdateCache put newly instantiated EdgeFetcher instance into guava cache, then call `onEvict` method defined in ResourceManager, which immediately call close() on Annoy4s JNI library, which causes the segmentation fault.

One quick fix on this issue is scheduling EdgeFetcher's close method in a short period of time delay in the background.