RFR: JDK8u: Add compatibility with -verbose:gc and -XX+TraceGenNTime GC options for logging

[Roman Kennke]

This makes Shenandoah in JDK8u pick up -verbose:gc and
-XX:+TraceGen0Time and -XX:+TraceGen1Time. The first prints information
for each GC phase, the latter two print the stats summary at the end.
We also print the summary for -verbose:gc. Ok to push?

http://cr.openjdk.java.net/~rkennke/jdk8u-logging/webrev.00/

Roman