code: @Override
      public ListInstancesResult listInstances(ListInstancesRequest request) {
          request = beforeClientExecution(request);
          return executeListInstances(request);
      }
docs: <p>
  Provides information for all active EC2 instances and EC2 instances terminated in the last 30 days, up to a
  maximum of 2,000. EC2 instances in any of the following states are considered active: AWAITING_FULFILLMENT,
  PROVISIONING, BOOTSTRAPPING, RUNNING.
  </p>
  
  @param listInstancesRequest
  This input determines which instances to list.
  @return Result of the ListInstances operation returned by the service.
  @throws InternalServerException
  This exception occurs when there is an internal failure in the EMR service.
  @throws InvalidRequestException
  This exception occurs when there is something wrong with user input.
  @sample AmazonElasticMapReduce.ListInstances
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/elasticmapreduce-2009-03-31/ListInstances" target="_top">AWS
  API Documentation</a>