RFR: 8184286: print_tracing_info() does not use Unified Logging for output

[Stefan Johansson]

Hi,

Please review this RFE to convert two more flags to use UL:
https://bugs.openjdk.java.net/browse/JDK-8184286

Webrev:
http://cr.openjdk.java.net/~sjohanss/8184286/hotspot.00/

Summary:
Converting two logging/tracing flags that had not been yet been changed 
to use unified logging. TraceYoungGenTime and TraceOldGenTime prints 
information at VM exit and the same information will now be available 
under tag-set "gc, heap, exit" on debug level.

Testing:
* Manually verified that same information as before is available.
* JPRT for sanity

Thanks,
Stefan