@Override
    public int compare(RegionPlan l, RegionPlan r) {
      return RegionPlan.compareTo(l, r);
    }
Stores the plan for the move of an individual region. Contains info for the region being moved,
info for the server the region should be moved from, and info for the server the region should be
moved to. The comparable implementation of this class compares only the region information and
not the source/dest server info.
hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/RegionPlan.java