RFR [8u]: Prettify Shenandoah JDK 8 logging

[Roman Kennke]

Very good! Let's do this!

Thanks,
Roman


> Webrev:
>   http://cr.openjdk.java.net/~shade/shenandoah/8u-logging-pretty/webrev.01/
> 
> Wanted to do this for a while now. Our 8u logging uses our own translation layer to use Unified
> Logging -like interface in Shenandoah code. However, that translation code produces weirdly
> formatted result, which complicates parsing/following GC logs that our adopters report. We can
> significantly improve that! It requires fiddling with the mess that C varargs are, but the
> improvement is worth it.
> 
> Logs before/after:
>   http://cr.openjdk.java.net/~shade/shenandoah/8u-logging-pretty/before.txt
>   http://cr.openjdk.java.net/~shade/shenandoah/8u-logging-pretty/after.txt
> 
> Testing: hotspot_gc_shenandoah; eyeballing GC logs with different logging options
>