Build JRuby with Java8

- this also makes sure JAVA_HOME is set to avoid issues with Maven

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Update jruby-benchmarks to include adapted harness

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Added first configuration draft for JRuby benchmarks

Signed-off-by: Stefan Marr <git@stefan-marr.de>