protected List<RegionInfo> randomRegions(int numRegions) {
    return randomRegions(numRegions, -1);
  }
This assumes the RegionPlan HSI instances are the same ones in the map, so actually no need to
even pass in the map, but I think it's clearer.
@return a list of all added {@link ServerAndLoad} values.
hbase-balancer/src/test/java/org/apache/hadoop/hbase/master/balancer/BalancerTestBase.java