static BalancerClusterState
    createMockBalancerClusterState(Map<ServerName, List<RegionInfo>> serverToRegions) {
    return new BalancerClusterState(serverToRegions, null, null, null, null);
  }
Partitions the given serverToRegions map by table The tables are derived from the RegionInfo
objects found in serverToRegions.
@param serverToRegions The map of servers to their assigned regions.
@return A map of tables to their server-to-region assignments.
hbase-balancer/src/test/java/org/apache/hadoop/hbase/master/balancer/CandidateGeneratorTestUtil.java