HBASE-29262 StochasticLoadBalancer should use the CostFunction epsilon when evaluating whether a move improved costs

Author: Ray Mattingly

hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/StochasticLoadBalancer.java

@@ -683,8 +683,10 @@ protected List<RegionPlan> balanceTable(TableName tableName,
 
       newCost = computeCost(cluster, currentCost);
 
+      double costImprovement = currentCost - newCost;
+      boolean costsImproved = costImprovement > CostFunction.getCostEpsilon(costImprovement);
       boolean conditionalsSimilarCostsImproved =
-        (newCost < currentCost && conditionalViolationsChange == 0 && !isViolatingConditionals);
+        (costsImproved && conditionalViolationsChange == 0 && !isViolatingConditionals);
       // Our first priority is to reduce conditional violations
       // Our second priority is to reduce balancer cost
       // change, regardless of cost change