HBASE-10263 make LruBlockCache single/multi/in-memory ratio user-configurable and provide preemptive mode for in-memory type block (Feng Honghua)

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.98@1557298 13f79535-47bb-0310-9956-ffa450edef68