RFR (S): 8151614: Improve logging in concurrent mark code

[Thomas Schatzl]

Hi all,

  can I have reviews for this change that improves the logging code for
concurrent mark by:

- removes the need to have two scoped objects, one for logging, one for
JFR for every phase
- tries to make the phase names correspond to method names
- add a "marking" tag to marking related log messages
- removes a duplicate log message ("Restart for overflow") at different
levels

CR:
https://bugs.openjdk.java.net/browse/JDK-8151614
Webrev:
http://cr.openjdk.java.net/~tschatzl/8151614/webrev/
Testing:
jprt


Thanks,
  Thomas