SPARK-4770. [DOC] [YARN] spark.scheduler.minRegisteredResourcesRatio doc...

[sryza]

...umented default is incorrect for YARN

[SparkQA]

Test build #24192 has started for PR 3624 at commit bd81a3a.

• This patch merges cleanly.

[SparkQA]

Test build #24192 has finished for PR 3624 at commit bd81a3a.

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

[AmplabJenkins]

Test PASSed.
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https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/24192/
Test PASSed.

[tgravescs]

+1. Thanks Sandy!

[tgravescs]

@pwendell is it ok to pull this doc change into 1.2?

[JoshRosen]

@tgravescs It should be fine to pull docs-only changes into branch-1.2. We're trying to hold off on merging code changes that aren't addressing 1.2.0 release blockers because we don't want to risk introducing new regressions and having to call new votes. If you do want to merge a code change that should eventually be backported into branch-1.2, just merge it into the other branches, leave its JIRA open with 1.2.1 listed in Target Version/s and not Fix Version/s, then add the backport-needed label to the issue so that we remember to come back to it after 1.2.0 is released.

[JoshRosen]

I grepped through the code and this LGTM, too, so I'm going to merge this into master and branch-1.2. Thanks @sryza!