[11u] RFR (S) 8221392: Reduce ConcurrentGCThreads spinning during start up

[Aleksey Shipilev]

Original RFE and change:
  https://bugs.openjdk.java.net/browse/JDK-8221392
  http://hg.openjdk.java.net/jdk/jdk/rev/2f522c487791

11u patch does not apply cleanly, because there is some context around patch is different in
mutexLocker.cpp. I applied the change by hand, and would like someone to eyeball it. Here:
  http://cr.openjdk.java.net/~shade/8221392/webrev.11u.01/

Testing: tier1

-- 
Thanks,
-Aleksey