在check_gpu时增加对当前环境可用设备的检查

[TracebaK]

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PR 变化内容类型 PR changes

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描述 Description

在check_gpu函数中补充了对当前环境可用设备的检查。在环境中安装了cuda版本的paddlepaddle，但没有可用的gpu时，默认使用cpu加载模型。

提PR之前的检查 Check-list

• [√] 这个 PR 是提交到dygraph分支或者是一个cherry-pick，否则请先提交到dygarph分支。
  This PR is pushed to the dygraph branch or cherry-picked from the dygraph branch. Otherwise, please push your changes to the dygraph branch.
• [√] 这个PR清楚描述了功能，帮助评审能提升效率。This PR have fully described what it does such that reviewers can speedup.
• [√] 这个PR已经经过本地测试。This PR can be convered by current tests or already test locally by you.

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[shiyutang]

@TracebaK 你好，请签署CLA～

[TracebaK]

@shiyutang CLA已签署~

[shiyutang]

LGTM