HOTFIX: Comment out YarnAllocatorSuite test case to fix broken build

[shivaram]

@sryza @tgravescs -- Let me know if you have a better fix

[SparkQA]

Test build #22631 has started for PR 3040 at commit e7820a2.

• This patch merges cleanly.

[shivaram]

I am going to close this in favor of #3041

[SparkQA]

Test build #22631 has finished for PR 3040 at commit e7820a2.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/22631/
Test PASSed.