Refine the unittest to support py38

[gfwm2013]

PR types

Bug fixes

PR changes

Others

Describe

Refine the unittests to support py38

在单测的运行中，paddle除了会抛出预期的的warnings之外，还会抛出一些其他的warnings，所以在运行一些会检测warning个数或是warning内容的单测的时候，就会报错。为了修改这个问题，作出本PR的修改。

For example:
单测: test_device_guard

warnings :

0 The Attr(force_cpu) of Op(fill_constant) will be deprecated in the future, please use 'device_guard' instead. 'device_guard' has higher priority when they are used at the same time.
1 an integer is required (got type paddle.fluid.core_avx.VarType).  Implicit conversion to integers using __int__ is deprecated, and may be removed in a future version of Python.
2 an integer is required (got type paddle.fluid.core_avx.op_proto_and_checker_maker.OpRole).  Implicit conversion to integers using __int__ is deprecated, and may be removed in a future version of Python.
3 an integer is required (got type paddle.fluid.core_avx.VarType).  Implicit conversion to integers using __int__ is deprecated, and may be removed in a future version of Python.
4 an integer is required (got type paddle.fluid.core_avx.op_proto_and_checker_maker.OpRole).  Implicit conversion to integers using __int__ is deprecated, and may be removed in a future version of Python.
5 The Attr(force_cpu) of Op(less_than) will be deprecated in the future, please use 'device_guard' instead. 'device_guard' has higher priority when they are used at the same time.
6 an integer is required (got type paddle.fluid.core_avx.op_proto_and_checker_maker.OpRole).  Implicit conversion to integers using __int__ is deprecated, and may be removed in a future version of Python.

在python3.8环境下运行test_device_guard这个单测，会得到上述7条warnings，但是其中只有2条（0 和 5）是我们所想要检测的。

[paddle-bot-old]

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

[zhhsplendid]

This PR LGTM but could you put more background on the PR description before merging?

From the code I think it is due to the difference of printed warning information, but could you state that in the PR description?

[zhangting2020]

LGTM

[zhhsplendid]

LGTM