Introduce DistributedTask abstraction enhancement for distributed executors

As we have requirements to add timeout, pluggable fail over policies, topology aware target selection policies to distributed executors we have to create a new abstraction DistributedTask that users can submit to DistributedExecutorService. We will provide builder for DistributedTask, keep the existing four submit methods in DistributedExecutorService and add four new methods with DistributedTask abstraction in place of Callable. See below:

interface DistributedExecutorService {
  … existing methods … 
    <T> List<Future<T>> submitEverywhere(DistributedTask<T> callable);
}

class DistributedTaskBuilder<T> {
   DistributedTaskBuilder<T> callable(Callable<T> callable);
   DistributedTaskBuilder<T> timeout(long t, TimeUnit tu);
   DistributedTaskBuilder<T> executionPolicy(DistributedExecutionPolicy p);
   DistributedTask<T> build();   
}