RFR (S) 8210724: Change the verbosity threshold of logging for [oopstorage, ref]

[Man Cao]

Hi all,

Could anyone review this logging change for oopstorage?
Webrev: http://cr.openjdk.java.net/~jcbeyler/8210724/webrev.00/
Bug: https://bugs.openjdk.java.net/browse/JDK-8210724

This is similar to the webrev I previously sent for
https://bugs.openjdk.java.net/browse/JDK-8210562. Kim mentioned it might be
reasonable to improve the logging in oopStorage.cpp. We discussed and
decided to create a separate issue for improving the logging.

The patch changes the logging level for [oopstorage,ref] to trace, and
consistently uses debug level for [oopstorage,blocks] and unusual events,
and uses log_info() for printing statistics. I think this would make the
logging for oopstorage more user-friendly.

Below is comparison of lines of messages:
$ java -Xlog:oopstorage*=<level> -Xms500m -Xmx500m -jar
dacapo-9.12-bach.jar tradesoap
                info   | debug  | trace
without patch:  107934 | 112990 | 112701
with patch:       1694 |   5247 | 112241

-Man
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