Benchmark JDK 11 vs JDK 8 on GeneralOptaPlannerBenchmarkApp

When JDK 8 was released we published a comparison between JDK 6, 7, and 8:
https://www.optaplanner.org/blog/2014/03/20/HowMuchFasterIsJava8.html

Now we should publish one between JDK 8 and JDK 11 (the others don't matter: below 8 doesn't run any more and JDK 9 and 10 are end of life).

Runs:

• JDK 8 (default - that is ParalelGC)
• JDK 11 with ParalelGC
• JDK 8 with G1
• JDK 11 (default - that is G1)

(you can also use the benchmark aggregator to merge those 4 benchmark reports if that's useful - run GeneralOptaPlannerBenchmarkApp with "--aggregator" as a process argument.)

Write a blog post for optaplanner.org:

• Start out by mentioning the average gain we got in JDK's 6 ->7 ->8, to introduce the research question of what speedup are we getting with JDK 11? – Link https://www.optaplanner.org/blog/2014/03/20/HowMuchFasterIsJava8.html
• Mention the importance of the garbage collector for an apples-to-apples comparison, throughput (ParellelGC) vs latency (G1)
  • Link https://www.optaplanner.org/blog/2015/07/31/WhatIsTheFastestGarbageCollectorInJava8.html

Adoc source of the how fast is java 8 article:
https://github.com/kiegroup/optaplanner-website/blob/master/blog/2014-03-20-HowMuchFasterIsJava8.adoc
Goal is to do a similar PR.