Add CompositeBucketCache to support tiered BC

LruBlockCache is not suitable in the following scenarios:
(1) cache size too large (will take too much heap memory, and evictBlocksByHfileName is not so efficient, as HBASE-23277 mentioned)
(2) block evicted frequently, especially cacheOnWrite & prefetchOnOpen are enabled.
Since block‘s data is reclaimed by GC, this may affect GC performance.
So how about enabling a Bucket based L1 Cache.