Release: use non-EOLed JDK version

[bzz]

JDK version that we are using for enry-java release is oracle JDK 8 which EOLed 1 year ago (and e.g is not available on newer linux 16.04 CI images any more)

This issue is about:

• update JDK to maintained LTS version e.g openJDK 11 (right now JDK 8 is used)
• update sbt version to 1.x, that works on newer JDK (current 0.13 does not)
• update sbt shell wrapper and plugin version, that support 1.0
• update build.sbt, adjusting for plugin changes (fat-jar assembly fails by default)
• make sure released version can be run on older JDK (one that Infra uses for the clusters)

Initial work was done under #221 but still a consensus on min JDK version is needed.

[smola]

@bzz We're using JDK 8 for Apache Spark. I'm not sure what the status on JDK 11 is, see SPARK-24417.