Skip test_cudnn_multiple_threads_same_device on ROCm (flaky) (#17061)

Skip test_cudnn_multiple_threads_same_device on ROCm (flaky) (#17061)

Summary:
cc iotamudelta
https://ci.pytorch.org/jenkins/job/pytorch-builds/job/py2-clang7-rocmdeb-ubuntu16.04-test/10722//console
https://ci.pytorch.org/jenkins/job/pytorch-builds/job/py2-clang7-rocmdeb-ubuntu16.04-test/10710//console
https://ci.pytorch.org/jenkins/job/pytorch-builds/job/py2-clang7-rocmdeb-ubuntu16.04-test/10753//console
https://ci.pytorch.org/jenkins/job/pytorch-builds/job/py2-devtoolset7-rocmrpm-centos7.5-test/1756//console
```
19:07:18 ======================================================================
19:07:18 FAIL: test_cudnn_multiple_threads_same_device (test_nn.TestNN)
19:07:18 ----------------------------------------------------------------------
19:07:18 Traceback (most recent call last):
19:07:18   File "/var/lib/jenkins/workspace/test/test_nn.py", line 3905, in test_cudnn_multiple_threads_same_device
19:07:18     (2048 - test_iters) * (2048 - test_iters))
19:07:18   File "/var/lib/jenkins/workspace/test/common_utils.py", line 453, in assertEqual
19:07:18     super(TestCase, self).assertLessEqual(abs(x - y), prec, message)
19:07:18 AssertionError: 3794704.0 not less than or equal to 1e-05 :
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17061

Differential Revision: D14069324

Pulled By: bddppq

fbshipit-source-id: e33b09abca217a62a8b577f9c332ea22985ef4ff