@Override
  public boolean setInstanceConfig(String clusterName, String instanceName, InstanceConfig instanceConfig) {
    setInstanceConfigCallCount++;
    removeDisabledReplicasIfNeeded(instanceConfig);
    instanceNameToInstanceConfigs.put(instanceName, instanceConfig);
    return true;
  }
Get the instances that have replicas for the given partition.
@param partition the partition name of the partition.
@return the set of instances that have replicas for this partition.
ambry-clustermap/src/test/java/com/github/ambry/clustermap/MockHelixAdmin.java