Backport Josh's correctness fixes

[ash211]

Lots of correctness stuff coming in over the past few days: https://issues.apache.org/jira/issues/?jql=project%20%3D%20SPARK%20AND%20reporter%20in%20(joshrosen)%20ORDER%20BY%20key%20DESC%2C%20priority%20DESC%2C%20updated%20DESC

• https://issues.apache.org/jira/browse/SPARK-22982
• https://issues.apache.org/jira/browse/SPARK-22983
• https://issues.apache.org/jira/browse/SPARK-22984
• https://issues.apache.org/jira/browse/SPARK-22985
• https://issues.apache.org/jira/browse/SPARK-22997

[robert3005]

All of them are already in master.