Java 9 breaks class loading

[Bathtor]

Using jdk-9 breaks javaassist 3.20.0-GA. At the very least it throws java.lang.RuntimeException: java.lang.ClassNotFoundException: se.sics.kompics.simulator.result.SimulationResultSingleton in its own test suite, but I've seen it complain about logging classes as well in the Kompics Scala suite.

I tried upgrading to javaassist 3.24.1-GA does not change a thing.

[Bathtor]

Ok, I fixed the test case within the simulator in 571a334, but that doesn't fix the actual issue. If I make the Scala Simulator depend on this it can't even load a bloody string, i.e. javassist.NotFoundException: java.lang.String
Something has very badly changed with class loaders and internal representation in java9, probably because of their silly modularisation.

[Bathtor]

Ok, so the stuff we did fixes Kompics Java Simulations on jdk9+, but Scala still has a bunch of issues.
Considering that Scala doesn't actually fully support anything above jdk8 and any version below Scala 2.13 (which is targeting jdk11 as the next LTS) probably never will (see scala/scala-dev#139), I say we table this until our dependencies catch up with jdk11 changes, then switch to 2.13 (or 2.14 if relevant) and see where we stand.
Until then, Kompics Scala is jdk8-only, at least for simulation support (though no idea what else may have broken there, that we didn't notice...at least the core tests run fine).

@o-alex If you agree, please merge the jdk9fix branch into master and do a new release tomorrow (and then mark this issue wontfix).