@Override
  public Object execute(Op op, int retries) {
    authenticateIfRequired(null, op);
    return executor.execute(op, retries);
  }
Execute the given op on the servers that this pool connects to. This method is responsible for
retrying the op if an attempt fails. It will only execute it once and on one server.

@param op the operation to execute
@param retries how many times to retry the operation
@return the result of execution if any; null if not
@since GemFire 5.7
geode-core/src/main/java/org/apache/geode/cache/client/internal/PoolImpl.java