RFR: 8277814: ConcurrentRefineThread should report rate when deactivating

[Kim Barrett]

Please review this change to the logging by concurrent refinement threads.
This change adds the cards processed per ms to the deactivation log message.

Testing:
mach5 tier1
locally ran a test with gc+refine=debug logging enabled and verified the
expected change to the deactivation log message.

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Commit messages:
 - log refinement rate

Changes: https://git.openjdk.java.net/jdk/pull/6550/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6550&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277814
  Stats: 17 lines in 3 files changed: 10 ins; 1 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6550.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6550/head:pull/6550

PR: https://git.openjdk.java.net/jdk/pull/6550