Use different slaves based on JDK version projects need

Use different slaves based on JDK version projects need

New base images for build servers with jdk8 and jdk11 are created
on City Nordix Tenant and Jenkins OpenStack Cloud Plugin is configured
to provision 1 slave for each jdk version we need.

JAVA_HOME is also set to same place in both base images so we don't
need to worry about overriding it manually.

New slaves are labelled with onap-build-ubuntu1604-jdk8 and onap-build-ubuntu1604-jdk11.
  https://jenkins.nordix.org/label/onap-build-ubuntu1604-jdk8/
  https://jenkins.nordix.org/label/onap-build-ubuntu1604-jdk11/

The old slave, base instance, and the base image will be removed from Jenkins
and from OpenStack tenant once the new image and slave are verified.

Change-Id: I7325088ed74f45acb4e12527ccf3ae16db4c5a51