Hi, All.

Thanks to your many many contributions,
Apache Spark master branch starts to pass on JDK11 as of today.
(with `hadoop-3.2` profile: Apache Hadoop 3.2 and Hive 2.3.6)

    (JDK11 is used for building and testing.)

We already verified all UTs (including PySpark/SparkR) before.

Please feel free to use JDK11 in order to build/test/run `master` branch and
share your experience including any issues. It will help Apache Spark 3.0.0 release.

For the follow-ups, please follow https://issues.apache.org/jira/browse/SPARK-24417 .
The next step is `how to support JDK8/JDK11 together in a single artifact`.