[ProcessGroup]add new comm primitive

[Baibaifan]

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Describe

1. Add new comm primitive (barrier\send\recv)

with _test_eager_guard():
    paddle.set_device('gpu:%d' %
                      paddle.distributed.ParallelEnv().dev_id)
    pg = init_process_group()
    # test barrier
    # rank 0
    if pg.rank() == 0:
        task = pg.barrier()

    # test send/recv
    # rank 0
    x = np.random.random(self.shape).astype(self.dtype)
    tensor_x = paddle.to_tensor(x)
    if pg.rank() == 0:
        task = pg.send(tensor_x, dst=1)
        task.wait()
        paddle.device.cuda.synchronize()
    # rank 1
    else:
        y = np.random.random(self.shape).astype(self.dtype)
        tensor_y = paddle.to_tensor(y)
        task = pg.recv(tensor_y, src=0)
        task.wait()
        paddle.device.cuda.synchronize()

[paddle-bot-old]

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[sandyhouse]

LGTM