RFR: 8151594: Move concurrent refinement thread activation logging out of GC pause

[Kim Barrett]

Please review this move of the thread activation logging by concurrent
refinment threads to be within the suspendible thread set context, rather
than before it.  This prevents the logging for the thread activation
sometimes being intermixed with GC pause-time logging.

Testing:
mach5 tier1

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Commit messages:
 - move thread active logging inside sts

Changes: https://git.openjdk.java.net/jdk/pull/6551/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6551&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8151594
  Stats: 9 lines in 1 file changed: 4 ins; 4 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6551.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6551/head:pull/6551

PR: https://git.openjdk.java.net/jdk/pull/6551