RFR: 8205664: Move detailed metaspace logging from debug to trace

[Per Liden]

Using -Xlog:gc*=debug typically provides extended GC information useful 
for GC debugging. Metaspace recently(?) started to log a lot of very 
detailed information (using gc+metaspace+...) on the debug level, making 
gc*=debug overly verbose. I propose that we move some of the detailed 
metaspace logging to the trace level.

Bug: https://bugs.openjdk.java.net/browse/JDK-8205664
Webrev: http://cr.openjdk.java.net/~pliden/8205664/webrev.0

/Per