Major Description
Similar to writing flush (HBASE-11511), compaction(HBASE-2231) to WAL and region open/close (HBASE-11512) , we should persist bulk load events to WAL.
This is especially important for secondary region replicas, since we can use this information to pick up primary regions' files from secondary replicas.
A design doc for secondary replica replication can be found at HBASE-11183.