RFR [8u]: Make sure -verbose:gc, PrintGC, PrintGCDetails work consistently

[Roman Kennke]

Am 07.09.2017 um 17:03 schrieb Aleksey Shipilev:
> http://cr.openjdk.java.net/~shade/shenandoah/8u-logging/webrev.01/
> 
> This is 8u-specific patch, because we have this logging compatibility layer there. We need to make
> sure -verbose:gc, PrintGC, PrintGCDetails work consistently there. Adds a test. Fixes another one.
> 
> Testing: hotspot_gc_shenandoah
> 
> Thanks,
> -Aleksey
> 

Looks good