RFR: Clean up Shenandoah configurations in shared tests

[Roman Kennke]

> On 10/11/2018 08:15 PM, Roman Kennke wrote:
>> What would happen if one tried to run a test that has
>> -XX:+UseShenandoahGC (e.g. next to UseCMS) in a build without
>> Shenandoah? Is there a way to predicate tests to only run in this config
>> if the config is actually present?
> 
> That would probably fail. We would need to test for that specially (later).

Ok. Push this clean up!

Thanks,
Roman