dygraph nccl init support host domain name

[danleifeng]

PR types

Bug fixes

PR changes

OPs

Describe

目前动态图nccl初始化时由于inet_pton函数只支持传入具体的ip地址，不支持传入域名，因此跑多机动态图任务（paddlecloud上）时程序会挂掉

if (inet_pton(AF_INET, ip, &serv_addr.sin_addr) <= 0) {
    PADDLE_THROW(platform::errors::Unavailable("Open address %s failed.", ep));
  }

解决方法：
在函数inet_pton前通过gethostbyname函数做解析

在paddlecloud上验证通过：

I1019 19:28:28.448112  1570 nccl_context.cc:105] nccl_context host: job-0bb5f8d7770b19f0-trainer-0.a5139f34-68ad-5528-8bb7-a906d3bfbf7b
I1019 19:28:28.453824  1570 nccl_context.cc:114] nccl_context host->ip: 10.127.31.20
...
I1019 19:28:28.453972  1570 nccl_context.cc:105] nccl_context host: job-0bb5f8d7770b19f0-trainer-1.a5139f34-68ad-5528-8bb7-a906d3bfbf7b
I1019 19:28:28.470842  1570 nccl_context.cc:114] nccl_context host->ip: 10.127.19.141
....

[paddle-bot-old]

Thanks for your contribution!
Please wait for the result of CI firstly. See Paddle CI Manual for details.

[zhiqiu]

LGTM