[SPARK-4730][YARN] Warn against deprecated YARN settings

See https://issues.apache.org/jira/browse/SPARK-4730.

Author: Andrew Or <andrew@databricks.com>

Closes #3590 from andrewor14/yarn-settings and squashes the following commits:

36e0753 [Andrew Or] Merge branch 'master' of github.com:apache/spark into yarn-settings
dcd1316 [Andrew Or] Warn against deprecated YARN settings

(cherry picked from commit 27c5399f4dd542e36ea579956b8cb0613de25c6d)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>