Base docker image is deprecated

Base image for Docker images is "fabric8/java-jboss-openjdk8-jdk", which is marked as deprecated (cf https://hub.docker.com/r/fabric8/java-jboss-openjdk8-jdk/ or https://github.com/fabric8io-images/java/pull/24).

fabric8/java-centos-openjdk8-jdk should be used instead.