HBASE-11942 Fix TestHRegionBusyWait
HBASE-11936 IsolationLevel must be attribute of a Query not a Scan (Vladimir Rodionov)
HBASE-11845 HFile tool should implement Tool, disable blockcache by default

HFileTool now accepts configuration via -D arguments. The blockcache is
disabled by default.
Run ReplicationSources and failover handlers with thread pools
Stop all retries after RecoverableZooKeeper#close