Disabled flaky test: test_mkldnn.test_activation

[lebeg]

Description

Disable flaky test: test_mkldnn.test_activation. Tracked in #12377

[pengzhao-intel]

Please refer the RCA in #12377 and wait a moment for the merge.
We need a better solution :)

[lebeg]

@pengzhao-intel Sure) But it's better to disable a flaky test first and so that PR's from others are not blocked and then add it again with a proper fix.

[lebeg]

We have continues failures on the CI for that:
http://jenkins.mxnet-ci.amazon-ml.com/blue/organizations/jenkins/incubator-mxnet/detail/master/1534/pipeline
http://jenkins.mxnet-ci.amazon-ml.com/blue/organizations/jenkins/incubator-mxnet/detail/master/1533/pipeline/

We need an urgent merge for this.

[pengzhao-intel]

@lebeg please see my comments on #12377.
Could you try to change eps number and run these cases again?

[lebeg]

@pengzhao-intel my intent with this PR is disabling the test, not to make it pass. As far as I have understood from #12377 @luobao-intel will submit a fix for the test soon and he could enable the test again in the same PR.

[lebeg]

Would that be alright with you @pengzhao-intel @luobao-intel?

[pengzhao-intel]

It's fine for us. Please go ahead.