code: public static <E> ServiceFuture<List<E>> fromPageResponse(Observable<ServiceResponse<Page<E>>> first, final Func1<String, Observable<ServiceResponse<Page<E>>>> next, final ListOperationCallback<E> callback) {
          final AzureServiceFuture<List<E>> serviceCall = new AzureServiceFuture<>();
          final PagingSubscriber<E> subscriber = new PagingSubscriber<>(serviceCall, next, callback);
          serviceCall.setSubscription(first
              .single()
              .subscribe(subscriber));
          return serviceCall;
      }
docs: Creates a ServiceCall from a paging operation.
  
  @param first the observable to the first page
  @param next the observable to poll subsequent pages
  @param callback the client-side callback
  @param <E> the element type
  @return the future based ServiceCall