RFC: Pick up 11.0.4+6 to sh/jdk11

[Roman Kennke]

Yep.

Thanks!
Roman

> Upstream published jdk-11.0.4+6, let's pick it up. It is just a handful of changes, so I would tag
> it shenandoah-jdk-11.0.4+6 immediately.
> 
> Changesets:
>   http://cr.openjdk.java.net/~shade/shenandoah/merges/jdk11-11.0.4%2b6/changesets.txt
> 
> Testing: hotspot_gc_shenandoah
>