private OperationTracker getOperationTracker(Properties props, boolean crossColoEnabled, int parallelism,
      RouterOperation routerOperation, boolean includeDownReplicas, boolean terminateOnNotFoundEnabled) {
    return getOperationTracker(props, crossColoEnabled, parallelism, routerOperation, includeDownReplicas,
        terminateOnNotFoundEnabled, true);
  }
Returns the right {@link OperationTracker} based on {@link #operationTrackerType}.
@param props {@link Properties} for {@link RouterConfig}.
@param crossColoEnabled {@code true} if cross colo needs to be enabled. {@code false} otherwise.
@param parallelism the number of parallel requests that can be in flight.
@param routerOperation the {@link RouterOperation} associate with this request.
@param includeDownReplicas whether to include down replicas in operation tracker.
@param terminateOnNotFoundEnabled whether to terminate the operation if we received not found responses.
@return the right {@link OperationTracker} based on {@link #operationTrackerType}.
ambry-router/src/test/java/com/github/ambry/router/OperationTrackerTest.java