[ZEPPELIN-6090] Drop JDK8 from CI

[Reamer]

What is this PR for?

This pull request removes the test with JDK 8. I have kept the JDK matrix to make it easier to switch to the next JDK later. The Livy integration tests have been removed as Livy does not currently support JDK 11. Take a look into, for more information https://lists.apache.org/thread/sk2hc5b5mg7t8sm8rc5mjg9v8n1ozwcz

What type of PR is it?

Improvement

What is the Jira issue?

• https://issues.apache.org/jira/browse/ZEPPELIN-6090

How should this be tested?

• CI

Questions:

• Does the license files need to update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No