private boolean unloadRegions(boolean unloadFromRack)
    throws ExecutionException, InterruptedException, TimeoutException {
    return unloadRegions(unloadFromRack, null);
  }
Unload regions from given {@link #hostname} using ack/noAck mode and {@link #maxthreads}.In
noAck mode we do not make sure that region is successfully online on the target region
server,hence it is best effort.We do not unload regions to hostnames given in
{@link #excludeFile}. If designatedFile is present with some contents, we will unload regions
to hostnames provided in {@link #designatedFile}. While unloading regions, destination
RegionServers are selected from different rack i.e regions should not move to any RegionServers
that belong to same rack as source RegionServer.
@return true if unloading succeeded, false otherwise
hbase-server/src/main/java/org/apache/hadoop/hbase/util/RegionMover.java